A high-yield, lossless chemical reaction conducted under ambient conditions is promising for green chemistry. However, owing to the sticky feature of liquids on solid surfaces and the high volatility of useful primary solvents, “droplet chemistry” is far from practical use. Thus, a droplet platform that prevents both droplet evaporation and adhesion losses is promising. Herein, we report a versatile method for droplet encapsulation with poly(octadecyl acrylate) (PODAc) based on the colloidosome technique. The PODAc colloidosomes are mechanochemically stable and thermally shape-reconfigurable while maintaining their surface omniphobicity. This feature enabled PODAc colloidosomes to load typical liquids regardless of their surface tension without experiencing evaporation or adhesion loss, transport like solid beads, and release inner liquid on-demand by heating or NIR light irradiation. The colloidosome is mass-producible and recyclable via a simple thermomechanical process. As a proof of concept, different droplet-scale reactions are demonstrated in colloidosomes using a volatile microliter solvent and volatile reactants.
{"title":"Droplet Green Chemistry Using Thermally Shape-Reconfigurable Omniphobic Colloidosomes","authors":"Karan Jain, Saurav Kumar, Manideepa Dhar, Haydar Ali, Nishanta Barman, Debasmita Sarkar, Mizuki Tenjimbayashi, Uttam Manna","doi":"10.1021/acs.chemmater.4c01261","DOIUrl":"https://doi.org/10.1021/acs.chemmater.4c01261","url":null,"abstract":"A high-yield, lossless chemical reaction conducted under ambient conditions is promising for green chemistry. However, owing to the sticky feature of liquids on solid surfaces and the high volatility of useful primary solvents, “droplet chemistry” is far from practical use. Thus, a droplet platform that prevents both droplet evaporation and adhesion losses is promising. Herein, we report a versatile method for droplet encapsulation with poly(octadecyl acrylate) (PODAc) based on the colloidosome technique. The PODAc colloidosomes are mechanochemically stable and thermally shape-reconfigurable while maintaining their surface omniphobicity. This feature enabled PODAc colloidosomes to load typical liquids regardless of their surface tension without experiencing evaporation or adhesion loss, transport like solid beads, and release inner liquid on-demand by heating or NIR light irradiation. The colloidosome is mass-producible and recyclable via a simple thermomechanical process. As a proof of concept, different droplet-scale reactions are demonstrated in colloidosomes using a volatile microliter solvent and volatile reactants.","PeriodicalId":33,"journal":{"name":"Chemistry of Materials","volume":null,"pages":null},"PeriodicalIF":8.6,"publicationDate":"2024-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141435966","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-21DOI: 10.1021/acs.chemmater.4c00928
Hrishit Banerjee, Clare P. Grey, Andrew J. Morris
Ni-rich LiNiaMnbCocO2 (NMC) cathodes undergo a series of degradation reactions, a prominent one being oxygen loss from the surface of the NMC particles; this process is more pronounced as Ni content is increased and at high voltages. Our first-principles study examines the redox behavior of transition metals (TMs) and O in Ni-rich NMC cathodes as a function of (de)lithiation. We use ab initio multiple scattering, density-functional theory (DFT)-based core-loss spectroscopy, and dynamical mean-field theory (DMFT) to give a many-body treatment of both dynamic and static correlations. Despite Ni, Mn, and Co K-edges calculated using ab initio multiple scattering based on Green’s functions showing an excellent match with experimentally obtained X-ray absorption near-edge spectra (XANES), we demonstrate that the ionic model of ascribing shifts in the XANES spectra to changes in metal oxidation states is inappropriate. We show that in these cases, which are characterized by strong covalency between the TM and oxygen, DMFT calculations based on Wannier projections are to date to the best of our knowledge the most accurate as well as computationally accessible method to calculate charges and hence assign oxidation states accurately. Due to the corresponding charge transfer from O p to Ni d, a ligand hole forms on O in Ni-rich regions. The individual Ni charge remains fairly constant throughout the charging/discharging process, particularly in Ni-rich environments in the material. In contrast, O has dual redox behavior, showing greater involvement in redox in Ni-rich regions while showing negligible redox involvement in Ni-poor regions. The Ni–O covalent system starts participating in redox around a state of delithiation of ∼17%, which represents, in our system, the beginning of the charge. Contrary to previous DFT calculations, we show that Co oxidation does not occur at the very end of charge but rather starts at an earlier state of delithiation of ∼67%. The dual behavior of O in terms of participation in the redox process helps explain the overall higher relative stability of lower Ni content NMCs compared to Ni-rich NMCs or LiNiO2 in terms of O loss and evolution of singlet oxygen.
富含镍的镍钴锰酸锂（NMC）阴极会发生一系列降解反应，其中最突出的反应是 NMC 粒子表面的氧气流失；随着镍含量的增加和在高电压条件下，这一过程会更加明显。我们的第一原理研究探讨了富镍 NMC 阴极中过渡金属 (TM) 和 O 的氧化还原行为与（脱）锂化的函数关系。我们利用 ab initio 多重散射、基于密度泛函理论 (DFT) 的磁芯损耗光谱和动态均场理论 (DMFT) 对动态和静态相关性进行了多体处理。尽管利用基于格林函数的非初始多重散射计算出的镍、锰和钴 K 边与实验获得的 X 射线吸收近边光谱 (XANES) 非常吻合，但我们证明了将 XANES 光谱中的偏移归因于金属氧化态变化的离子模型是不恰当的。我们的研究表明，在这些以 TM 和氧之间的强共价性为特征的情况下，基于 Wannier 投影的 DMFT 计算是迄今为止我们所知的最准确、最易计算的方法，可用于计算电荷，从而准确地分配氧化态。由于相应的电荷从 O p 转移到 Ni d，在富镍区域的 O 上形成了一个配体空穴。在整个充电/放电过程中，单个镍电荷保持相当稳定，尤其是在材料中的富镍环境中。与此相反，O 具有双重氧化还原行为，在富镍区域参与氧化还原的程度更高，而在贫镍区域参与氧化还原的程度几乎可以忽略不计。Ni-O 共价体系在脱硫化程度达到 ∼17% 左右时开始参与氧化还原，在我们的体系中，这代表着电荷的开始。与之前的 DFT 计算相反，我们发现钴的氧化作用并不是发生在电荷的最末端，而是开始于较早的∼67% 的脱硫化状态。在参与氧化还原过程方面，O 的双重行为有助于解释为什么与富含镍的 NMC 或 LiNiO2 相比，镍含量较低的 NMC 在 O 损失和单线态氧演化方面具有更高的相对稳定性。
{"title":"Stability and Redox Mechanisms of Ni-Rich NMC Cathodes: Insights from First-Principles Many-Body Calculations","authors":"Hrishit Banerjee, Clare P. Grey, Andrew J. Morris","doi":"10.1021/acs.chemmater.4c00928","DOIUrl":"https://doi.org/10.1021/acs.chemmater.4c00928","url":null,"abstract":"Ni-rich LiNi<sub><i>a</i></sub>Mn<sub><i>b</i></sub>Co<sub><i>c</i></sub>O<sub>2</sub> (NMC) cathodes undergo a series of degradation reactions, a prominent one being oxygen loss from the surface of the NMC particles; this process is more pronounced as Ni content is increased and at high voltages. Our first-principles study examines the redox behavior of transition metals (TMs) and O in Ni-rich NMC cathodes as a function of (de)lithiation. We use ab initio multiple scattering, density-functional theory (DFT)-based core-loss spectroscopy, and dynamical mean-field theory (DMFT) to give a many-body treatment of both dynamic and static correlations. Despite Ni, Mn, and Co K-edges calculated using ab initio multiple scattering based on Green’s functions showing an excellent match with experimentally obtained X-ray absorption near-edge spectra (XANES), we demonstrate that the ionic model of ascribing shifts in the XANES spectra to changes in metal oxidation states is inappropriate. We show that in these cases, which are characterized by strong covalency between the TM and oxygen, DMFT calculations based on Wannier projections are to date to the best of our knowledge the most accurate as well as computationally accessible method to calculate charges and hence assign oxidation states accurately. Due to the corresponding charge transfer from O p to Ni d, a ligand hole forms on O in Ni-rich regions. The individual Ni charge remains fairly constant throughout the charging/discharging process, particularly in Ni-rich environments in the material. In contrast, O has dual redox behavior, showing greater involvement in redox in Ni-rich regions while showing negligible redox involvement in Ni-poor regions. The Ni–O covalent system starts participating in redox around a state of delithiation of ∼17%, which represents, in our system, the beginning of the charge. Contrary to previous DFT calculations, we show that Co oxidation does not occur at the very end of charge but rather starts at an earlier state of delithiation of ∼67%. The dual behavior of O in terms of participation in the redox process helps explain the overall higher relative stability of lower Ni content NMCs compared to Ni-rich NMCs or LiNiO<sub>2</sub> in terms of O loss and evolution of singlet oxygen.","PeriodicalId":33,"journal":{"name":"Chemistry of Materials","volume":null,"pages":null},"PeriodicalIF":8.6,"publicationDate":"2024-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141441637","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-21DOI: 10.1021/acs.chemmater.4c00490
Seong Shik Kim, David N. Agyeman-Budu, Joshua J. Zak, Jessica L. Andrews, Jonathan Li, Brent C. Melot, Johanna Nelson Weker, Kimberly A. See
New energy storage methods are emerging to increase the energy density of state-of-the-art battery systems beyond conventional intercalation electrode materials. For instance, employing anion redox can yield higher capacities compared with transition metal redox alone. Anion redox in sulfides has been recognized since the early days of rechargeable battery research. Here, we study the effect of d–p overlap in controlling anion redox by shifting the metal d band position relative to the S p band. We aim to determine the effect of shifting the d band position on the electronic structure and, ultimately, on charge compensation. Two isostructural sulfides LiNaFeS2 and LiNaCoS2 are directly compared to the hypothesis that the Co material should yield more covalent metal–anion bonds. LiNaCoS2 exhibits a multielectron capacity of ≥1.7 electrons per formula unit, but despite the lowered Co d band, the voltage of anion redox is close to that of LiNaFeS2. Interestingly, the material suffers from rapid capacity fade. Through a combination of solid-state nuclear magnetic resonance spectroscopy, Co and S X-ray absorption spectroscopy, X-ray diffraction, and partial density of states calculations, we demonstrate that oxidation of S nonbonding p states to S22– occurs in early states of charge, which leads to an irreversible phase transition. We conclude that the lower energy of Co d bands increases their overlap with S p bands while maintaining S nonbonding p states at the same higher energy level, thus causing no alteration in the oxidation potential. Further, the higher crystal field stabilization energy for octahedral coordination over tetrahedral coordination is proposed to cause the irreversible phase transition in LiNaCoS2.
除了传统的插层电极材料外，新的能量存储方法也在不断涌现，以提高最先进电池系统的能量密度。例如，与单独使用过渡金属氧化还原法相比，使用阴离子氧化还原法可以产生更高的容量。硫化物中的阴离子氧化还原早在充电电池研究初期就已得到认可。在此，我们研究了通过移动金属 d 波段与 S p 波段的相对位置来控制阴离子氧化还原的 d-p 重叠效果。我们旨在确定 d 带位置移动对电子结构的影响，并最终确定对电荷补偿的影响。我们直接比较了两种同结构硫化物 LiNaFeS2 和 LiNaCoS2，并假设钴材料应产生更多的共价金属阴离子键。LiNaCoS2 每式单位的多电子容量≥1.7 个电子，但尽管 Co d 带降低，阴离子氧化还原电压却接近 LiNaFeS2。有趣的是，这种材料的容量衰减很快。通过结合固态核磁共振光谱、Co 和 S X 射线吸收光谱、X 射线衍射和部分态密度计算，我们证明了 S 非键 p 态氧化为 S22- 发生在电荷的早期状态，这导致了不可逆的相变。我们的结论是，Co d 带的能量较低，增加了它们与 S p 带的重叠，同时将 S 非键 p 态保持在相同的较高能量水平，因此不会改变氧化势。此外，八面体配位比四面体配位具有更高的晶场稳定能，这也是导致钴酸锂发生不可逆相变的原因。
{"title":"Effect of Metal d Band Position on Anion Redox in Alkali-Rich Sulfides","authors":"Seong Shik Kim, David N. Agyeman-Budu, Joshua J. Zak, Jessica L. Andrews, Jonathan Li, Brent C. Melot, Johanna Nelson Weker, Kimberly A. See","doi":"10.1021/acs.chemmater.4c00490","DOIUrl":"https://doi.org/10.1021/acs.chemmater.4c00490","url":null,"abstract":"New energy storage methods are emerging to increase the energy density of state-of-the-art battery systems beyond conventional intercalation electrode materials. For instance, employing anion redox can yield higher capacities compared with transition metal redox alone. Anion redox in sulfides has been recognized since the early days of rechargeable battery research. Here, we study the effect of <i>d–p</i> overlap in controlling anion redox by shifting the metal <i>d</i> band position relative to the S <i>p</i> band. We aim to determine the effect of shifting the <i>d</i> band position on the electronic structure and, ultimately, on charge compensation. Two isostructural sulfides LiNaFeS<sub>2</sub> and LiNaCoS<sub>2</sub> are directly compared to the hypothesis that the Co material should yield more covalent metal–anion bonds. LiNaCoS<sub>2</sub> exhibits a multielectron capacity of ≥1.7 electrons per formula unit, but despite the lowered Co <i>d</i> band, the voltage of anion redox is close to that of LiNaFeS<sub>2</sub>. Interestingly, the material suffers from rapid capacity fade. Through a combination of solid-state nuclear magnetic resonance spectroscopy, Co and S X-ray absorption spectroscopy, X-ray diffraction, and partial density of states calculations, we demonstrate that oxidation of S nonbonding <i>p</i> states to S<sub arrange=\"stagger\">2</sub><sup arrange=\"stagger\">2–</sup> occurs in early states of charge, which leads to an irreversible phase transition. We conclude that the lower energy of Co <i>d</i> bands increases their overlap with S <i>p</i> bands while maintaining S nonbonding <i>p</i> states at the same higher energy level, thus causing no alteration in the oxidation potential. Further, the higher crystal field stabilization energy for octahedral coordination over tetrahedral coordination is proposed to cause the irreversible phase transition in LiNaCoS<sub>2</sub>.","PeriodicalId":33,"journal":{"name":"Chemistry of Materials","volume":null,"pages":null},"PeriodicalIF":8.6,"publicationDate":"2024-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141435958","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-21DOI: 10.1021/acs.chemmater.4c00379
Ryan H. Manso, Jiyun Hong, Wei Wang, Prashant Acharya, Adam S. Hoffman, Xiao Tong, Feng Wang, Lauren F. Greenlee, Yimei Zhu, Simon R. Bare, Jingyi Chen
Metal phosphide-containing materials have emerged as a potential candidate of nonprecious metal-based catalysts for alkaline oxygen evolution reaction (OER). While it is known that metal phosphide undergoes structural evolution, considerable debate persists regarding the effects of dynamics on the surface activation and morphological stability of the catalysts. In this study, we synthesize NiPx-FeOx core–shell nanocatalysts with an amorphous NiPx core designed for enhanced OER activity. Using ex situ X-ray absorption spectroscopy, we elucidate the local structural changes as a function of the cyclic voltammetry cycles. Our studies suggest that the presence of corner-sharing octahedra in the FeOx shell improves structural rigidity through interlayer cross-linking, thereby inhibiting the diffusion of OH–/H2O. Thus, the FeOx shell preserves the amorphous NiPx core from rapid oxidation to Ni3(PO4)2 and Ni(OH)2. On the other hand, the incorporation of Ni from the core into the FeOx shell facilitates absorption of hydroxide ions for OER. As a result, Ni/Fe(OH)x at the surface oxidizes to the active γ-(oxy)hydroxide phase under the applied potentials, promoting OER. This intriguing synergistic behavior holds significance as such a synthetic route involving the FeOx shell can be extended to other systems, enabling manipulation of surface adsorption and diffusion of hydroxide ions. These findings also demonstrate that nanomaterials with core–shell morphologies can be tuned to leverage the strength of each metallic component for improved electrochemical activities.
含磷化金属的材料已成为碱性氧进化反应（OER）非贵金属基催化剂的潜在候选材料。众所周知，金属磷化物会发生结构演化，但关于动力学对催化剂表面活化和形态稳定性的影响仍存在很大争议。在本研究中，我们合成了具有无定形 NiPx 内核的 NiPx-FeOx 核壳纳米催化剂，以增强 OER 活性。利用原位 X 射线吸收光谱，我们阐明了局部结构变化与循环伏安法周期的函数关系。我们的研究表明，FeOx 外壳中分角八面体的存在通过层间交联提高了结构的刚性，从而抑制了 OH-/H2O 的扩散。因此，FeOx 外壳可以保护无定形的 NiPx 内核不被快速氧化成 Ni3(PO4)2 和 Ni(OH)2。另一方面，内核中的 Ni 与氧化铁外壳的结合促进了氢氧根离子的吸收，从而实现 OER。因此，表面的 Ni/Fe(OH)x 在施加的电位下会氧化成活性的 γ-（氧）氢氧化物相，从而促进 OER。这种有趣的协同行为具有重要意义，因为这种涉及氧化铁外壳的合成路线可以扩展到其他系统，从而可以操纵氢氧根离子的表面吸附和扩散。这些发现还表明，可以对具有核壳形态的纳米材料进行调整，以利用每种金属成分的强度来提高电化学活性。
{"title":"Revealing Structural Evolution of Nickel Phosphide-Iron Oxide Core–Shell Nanocatalysts in Alkaline Medium for the Oxygen Evolution Reaction","authors":"Ryan H. Manso, Jiyun Hong, Wei Wang, Prashant Acharya, Adam S. Hoffman, Xiao Tong, Feng Wang, Lauren F. Greenlee, Yimei Zhu, Simon R. Bare, Jingyi Chen","doi":"10.1021/acs.chemmater.4c00379","DOIUrl":"https://doi.org/10.1021/acs.chemmater.4c00379","url":null,"abstract":"Metal phosphide-containing materials have emerged as a potential candidate of nonprecious metal-based catalysts for alkaline oxygen evolution reaction (OER). While it is known that metal phosphide undergoes structural evolution, considerable debate persists regarding the effects of dynamics on the surface activation and morphological stability of the catalysts. In this study, we synthesize NiP<sub><i>x</i></sub>-FeO<sub><i>x</i></sub> core–shell nanocatalysts with an amorphous NiP<sub><i>x</i></sub> core designed for enhanced OER activity. Using <i>ex situ</i> X-ray absorption spectroscopy, we elucidate the local structural changes as a function of the cyclic voltammetry cycles. Our studies suggest that the presence of corner-sharing octahedra in the FeO<sub><i>x</i></sub> shell improves structural rigidity through interlayer cross-linking, thereby inhibiting the diffusion of OH<sup>–</sup>/H<sub>2</sub>O. Thus, the FeO<sub><i>x</i></sub> shell preserves the amorphous NiP<sub><i>x</i></sub> core from rapid oxidation to Ni<sub>3</sub>(PO<sub>4</sub>)<sub>2</sub> and Ni(OH)<sub>2</sub>. On the other hand, the incorporation of Ni from the core into the FeO<sub><i>x</i></sub> shell facilitates absorption of hydroxide ions for OER. As a result, Ni/Fe(OH)<sub><i>x</i></sub> at the surface oxidizes to the active γ-(oxy)hydroxide phase under the applied potentials, promoting OER. This intriguing synergistic behavior holds significance as such a synthetic route involving the FeO<sub><i>x</i></sub> shell can be extended to other systems, enabling manipulation of surface adsorption and diffusion of hydroxide ions. These findings also demonstrate that nanomaterials with core–shell morphologies can be tuned to leverage the strength of each metallic component for improved electrochemical activities.","PeriodicalId":33,"journal":{"name":"Chemistry of Materials","volume":null,"pages":null},"PeriodicalIF":8.6,"publicationDate":"2024-06-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141436112","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-20DOI: 10.1021/acs.chemmater.4c00809
Soumita Chakraborty, Daizy Kalita, Sakshi Agarwal, Surishi Vashishth, Nijita Mathew, Sisir Maity, Devender Goud, Ankit Rao, Sebastian C. Peter, Abhishek K. Singh, Muthusamy Eswaramoorthy
Electrochemical H2 generation and CO2 reduction address the energy and environmental crisis plaguing the world. An efficient electrocatalyst would require the lowest overpotential for these reactions. Given its position on the volcano plot near platinum, palladium presents itself as a viable alternative for the hydrogen evolution reaction (HER). However, the activity is limited by a high overpotential. It is also a good electrocatalyst for the CO2 reduction reaction (CO2RR) due to the favorable position of the d-band center. Nevertheless, the CO poisoning of the active site results in low electrocatalytic stability. Herein, we report a Ni-incorporated palladium catalyst, NiPd, which reduces water to H2 at a very low overpotential of 25 mV (η10). Furthermore, it reduces CO2 to formate with a very high faradaic efficiency of 97% at a potential of −0.25 V (vs RHE). DFT studies show that Ni inclusion leads to the facile activation of CO2 due to a bent adsorption configuration at the catalyst surface. The NiPd catalyst exhibits a strong and stable performance for HER (400 h) as well as for CO2RR (9 h) with high structural integrity as proven by postreaction characterization studies.
电化学制取 H2 和减少 CO2 可解决困扰全球的能源和环境危机。高效的电催化剂要求这些反应具有最低的过电位。鉴于钯在火山图上的位置接近铂，因此钯是氢进化反应（HER）的可行替代品。不过，其活性受到高过电位的限制。由于 d 带中心的有利位置，钯还是二氧化碳还原反应（CO2RR）的良好电催化剂。然而，活性位点的 CO 中毒导致电催化稳定性较低。在此，我们报告了一种掺入镍的钯催化剂 NiPd，它能在 25 mV (η10) 的超低过电位下将水还原成 H2。此外，它还能在 -0.25 V 的电位（相对于 RHE）下将 CO2 还原成甲酸盐，远化效率高达 97%。DFT 研究表明，由于催化剂表面的弯曲吸附构型，镍的加入使 CO2 易于活化。经反应后表征研究证明，NiPd 催化剂在 HER（400 小时）和 CO2RR（9 小时）中表现出强大而稳定的性能，并具有较高的结构完整性。
{"title":"Tuning the Electrocatalytic Activity of Pd Nanocatalyst toward Hydrogen Evolution and Carbon Dioxide Reduction Reactions by Nickel Incorporation","authors":"Soumita Chakraborty, Daizy Kalita, Sakshi Agarwal, Surishi Vashishth, Nijita Mathew, Sisir Maity, Devender Goud, Ankit Rao, Sebastian C. Peter, Abhishek K. Singh, Muthusamy Eswaramoorthy","doi":"10.1021/acs.chemmater.4c00809","DOIUrl":"https://doi.org/10.1021/acs.chemmater.4c00809","url":null,"abstract":"Electrochemical H<sub>2</sub> generation and CO<sub>2</sub> reduction address the energy and environmental crisis plaguing the world. An efficient electrocatalyst would require the lowest overpotential for these reactions. Given its position on the volcano plot near platinum, palladium presents itself as a viable alternative for the hydrogen evolution reaction (HER). However, the activity is limited by a high overpotential. It is also a good electrocatalyst for the CO<sub>2</sub> reduction reaction (CO<sub>2</sub>RR) due to the favorable position of the d-band center. Nevertheless, the CO poisoning of the active site results in low electrocatalytic stability. Herein, we report a Ni-incorporated palladium catalyst, NiPd, which reduces water to H<sub>2</sub> at a very low overpotential of 25 mV (η<sub>10</sub>). Furthermore, it reduces CO<sub>2</sub> to formate with a very high faradaic efficiency of 97% at a potential of −0.25 V (vs RHE). DFT studies show that Ni inclusion leads to the facile activation of CO<sub>2</sub> due to a bent adsorption configuration at the catalyst surface. The NiPd catalyst exhibits a strong and stable performance for HER (400 h) as well as for CO<sub>2</sub>RR (9 h) with high structural integrity as proven by postreaction characterization studies.","PeriodicalId":33,"journal":{"name":"Chemistry of Materials","volume":null,"pages":null},"PeriodicalIF":8.6,"publicationDate":"2024-06-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141435969","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-19DOI: 10.1021/acs.chemmater.4c00694
Maximilian A. Plass, Sebastian Bette, Christian Schneider, Roland Eger, Bettina V. Lotsch
The structure family of perovskites and related phases contains a large variety of compounds with versatile properties and applications. While perovskite structures of the AIBIIX3 type usually are categorized based on geometrical considerations like the Goldschmidt tolerance factor, perovskite-related and distorted structure types need to be classified by the more general approach of structure field diagrams. By synthesizing LiSr2X5 with X = Cl, Br, and I, LiSr2Br3.9Cl1.1 and LiEu2X5 with X = Br and I, and LiSm2I5 and LiMIII3 with MII = Sr, Ba, Eu, and Sm as well as KCdBr3, we were able to add several new compounds exhibiting different structure types to the structure field diagrams of perovskite-related ABX3 and BIA2IIX5 compounds. According to the size of lithium ions, these compounds exhibit inverse structure types of BIAIIX3 or BIA2IIX5, where the monovalent lithium ion resides on the lower-coordinated B-site and the divalent metal cation occupies the higher-coordinated A-site. Using in situ variable-temperature powder X-ray diffraction and differential scanning calorimetry, we investigated the relationship between different structure types exemplarily for LiEuI3. Additionally, we examined the ionic transport properties of the different structure types by means of electrochemical impedance spectroscopy and bond valence sum calculations and found restricted dimensionalities of the ion percolation pathways in the investigated structure types, generally limiting the ionic transport properties. Furthermore, the size and softness of the underlying anion lattice, as well as the size and bonding situation of the divalent metal cations, can influence the charge transport properties in LiM2X5 and LiMX3 compounds significantly, where ionic conductivities range between 10–12 and 10–7 S cm–1 at 25 °C.
包晶石及相关相的结构家族包含了大量具有多种特性和应用的化合物。AIBIIX3 类型的包晶结构通常是根据戈德施密特公差因子等几何因素进行分类的，而与包晶相关的扭曲结构类型则需要通过结构场图这一更为通用的方法进行分类。通过合成 X = Cl、Br 和 I 的 LiSr2X5、X = Br 和 I 的 LiSr2Br3.9Cl1.1 和 LiEu2X5、MII = Sr、Ba、Eu 和 Sm 的 LiSm2I5 和 LiMIII3 以及 KCdBr3，我们能够在透辉石相关 ABX3 和 BIA2IIX5 化合物的结构场图中添加几种表现出不同结构类型的新化合物。根据锂离子的大小，这些化合物呈现出 BIAIIX3 或 BIA2IIX5 的反向结构类型，其中一价锂离子位于低配位的 B 位上，而二价金属阳离子则位于高配位的 A 位上。利用原位变温粉末 X 射线衍射和差示扫描量热法，我们以 LiEuI3 为例，研究了不同结构类型之间的关系。此外，我们还通过电化学阻抗谱和键价和计算研究了不同结构类型的离子传输特性，发现所研究结构类型中离子渗流路径的维度有限，普遍限制了离子传输特性。此外，底层阴离子晶格的大小和软度，以及二价金属阳离子的大小和成键情况，都会对 LiM2X5 和 LiMX3 化合物的电荷传输特性产生重大影响，这两种化合物在 25 °C 时的离子电导率介于 10-12 和 10-7 S cm-1 之间。
{"title":"Structures and Ionic Transport Properties of Perovskite-Related BIAIIX3 and BIA2IIX5 Halides","authors":"Maximilian A. Plass, Sebastian Bette, Christian Schneider, Roland Eger, Bettina V. Lotsch","doi":"10.1021/acs.chemmater.4c00694","DOIUrl":"https://doi.org/10.1021/acs.chemmater.4c00694","url":null,"abstract":"The structure family of perovskites and related phases contains a large variety of compounds with versatile properties and applications. While perovskite structures of the <i>A</i><sup>I</sup><i>B</i><sup>II</sup><i>X</i><sub>3</sub> type usually are categorized based on geometrical considerations like the Goldschmidt tolerance factor, perovskite-related and distorted structure types need to be classified by the more general approach of structure field diagrams. By synthesizing LiSr<sub>2</sub><i>X</i><sub>5</sub> with <i>X</i> = Cl, Br, and I, LiSr<sub>2</sub>Br<sub>3.9</sub>Cl<sub>1.1</sub> and LiEu<sub>2</sub><i>X</i><sub>5</sub> with <i>X</i> = Br and I, and LiSm<sub>2</sub>I<sub>5</sub> and Li<i>M</i><sup>II</sup>I<sub>3</sub> with <i>M</i><sup>II</sup> = Sr, Ba, Eu, and Sm as well as KCdBr<sub>3</sub>, we were able to add several new compounds exhibiting different structure types to the structure field diagrams of perovskite-related <i>ABX</i><sub>3</sub> and <i>B</i><sup>I</sup><i>A</i><sub>2</sub><sup>II</sup><i>X</i><sub>5</sub> compounds. According to the size of lithium ions, these compounds exhibit inverse structure types of <i>B</i><sup>I</sup><i>A</i><sup>II</sup><i>X</i><sub>3</sub> or <i>B</i><sup>I</sup><i>A</i><sub>2</sub><sup>II</sup><i>X</i><sub>5</sub>, where the monovalent lithium ion resides on the lower-coordinated <i>B</i>-site and the divalent metal cation occupies the higher-coordinated <i>A</i>-site. Using <i>in situ</i> variable-temperature powder X-ray diffraction and differential scanning calorimetry, we investigated the relationship between different structure types exemplarily for LiEuI<sub>3</sub>. Additionally, we examined the ionic transport properties of the different structure types by means of electrochemical impedance spectroscopy and bond valence sum calculations and found restricted dimensionalities of the ion percolation pathways in the investigated structure types, generally limiting the ionic transport properties. Furthermore, the size and softness of the underlying anion lattice, as well as the size and bonding situation of the divalent metal cations, can influence the charge transport properties in Li<i>M</i><sub>2</sub><i>X</i><sub>5</sub> and Li<i>MX</i><sub>3</sub> compounds significantly, where ionic conductivities range between 10<sup>–12</sup> and 10<sup>–7</sup> S cm<sup>–1</sup> at 25 °C.","PeriodicalId":33,"journal":{"name":"Chemistry of Materials","volume":null,"pages":null},"PeriodicalIF":8.6,"publicationDate":"2024-06-19","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141435894","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-18DOI: 10.1021/acs.chemmater.4c00536
Savi Chaudhary, Ramaswamy Murugavel
Heterometal phosphates are burgeoning electrocatalysts and cathode materials in energy storage and conversion devices. In this work, we demonstrate a novel and clean synthetic route for substoichiometric lithium-deficient metastable Cmcm-Li0.65(7)Co1.16(2)PO4 (Li-Co-P-HEX) and metaphosphate P212121-LiCo(PO3)3 (Li-Co-P-BT), starting from the same starting material [LiCo(dtbp)3] (dtbp = di-tert-butyl phosphate) through a thermolytic single-source precursor approach. The heterometal organophosphate [LiCo(dtbp)3] decomposed into different phases of inorganic heterometal phosphates by employing a solution and solid-state thermal treatment. The solution-processed Li-deficient orthophosphate exhibits superior oxygen evolution reaction activity, delivering a current density of 10 mA cm–2 at an overpotential of 294 mV, outperforming other reported lithium–cobalt phosphates for water oxidation. The enhanced performance of the Cmcm-Li0.65(7)Co1.16(2)PO4 as an electrocatalyst elucidates the synergistic effect generated by the structure, composition, and morphology.
{"title":"Thermally Labile Organic-Soluble Heterometal Diorganophosphate-Derived Efficient Electrocatalysts for the Oxygen Evolution Reaction","authors":"Savi Chaudhary, Ramaswamy Murugavel","doi":"10.1021/acs.chemmater.4c00536","DOIUrl":"https://doi.org/10.1021/acs.chemmater.4c00536","url":null,"abstract":"Heterometal phosphates are burgeoning electrocatalysts and cathode materials in energy storage and conversion devices. In this work, we demonstrate a novel and clean synthetic route for substoichiometric lithium-deficient metastable <i>Cmcm</i>-Li<sub>0.65(7)</sub>Co<sub>1.16(2)</sub>PO<sub>4</sub> (<b>Li-Co-P-HEX</b>) and metaphosphate <i>P</i>2<sub>1</sub>2<sub>1</sub>2<sub>1</sub>-LiCo(PO<sub>3</sub>)<sub>3</sub> (<b>Li-Co-P-BT</b>), starting from the same starting material [LiCo(dtbp)<sub>3</sub>] (dtbp = di-<i>tert</i>-butyl phosphate) through a thermolytic single-source precursor approach. The heterometal organophosphate [LiCo(dtbp)<sub>3</sub>] decomposed into different phases of inorganic heterometal phosphates by employing a solution and solid-state thermal treatment. The solution-processed Li-deficient orthophosphate exhibits superior oxygen evolution reaction activity, delivering a current density of 10 mA cm<sup>–2</sup> at an overpotential of 294 mV, outperforming other reported lithium–cobalt phosphates for water oxidation. The enhanced performance of the <i>Cmcm</i>-Li<sub>0.65(7)</sub>Co<sub>1.16(2)</sub>PO<sub>4</sub> as an electrocatalyst elucidates the synergistic effect generated by the structure, composition, and morphology.","PeriodicalId":33,"journal":{"name":"Chemistry of Materials","volume":null,"pages":null},"PeriodicalIF":8.6,"publicationDate":"2024-06-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141436181","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-18DOI: 10.1021/acs.chemmater.4c00178
Kamil Czelej, Mubashir Mansoor, Mehmet Ali Sarsil, Mert Tas, Yahya A. Sorkhe, Mehya Mansoor, Maryam Mansoor, Bora Derin, Onur Ergen, Servet Timur, Mustafa Ürgen
GaN is a technologically indispensable material for various optoelectronic properties, mainly due to the dopant-induced or native atomic-scale point defects that can create single photon emitters, a range of luminescence bands, and n- or p-type conductivities. Among the various dopants, chromium and manganese-induced defects have been of particular interest over the past few years, because some of them contribute to our present-day light-emitting diode (LED) and spintronic technologies. However, the nature of such atomistic centers in Cr and Mn-doped GaN is yet to be understood. A comprehensive defect thermodynamic analysis of Cr- and Mn-induced defects is essential for their engineering in GaN crystals because by mapping out the defect stabilities as a function of crystal growth parameters, we can maximize the concentration of the target point defects. We therefore investigate chromium and manganese-induced defects in GaN with ab initio methods using the highly accurate exchange–correlation hybrid functionals, and the phase transformations upon excess incorporation of these dopants using the CALPHAD method. We also investigate the impact of oxygen codoping that can be unintentionally incorporated during crystal growth. Our analysis sheds light on the atomistic cause of the unintentional n-type conductivity in GaN, being ON-related. In the case of Cr doping, the formation of CrGa defects is the most dominant, with an E+/0 charge transition at EVBM + 2.19 eV. Increasing nitrogen partial pressure tends to enhance the concentration of CrGa. However, in the case of doping with Mn, several different Mn-related centers can form depending on the growth conditions, with MnGa being the most dominant. MnGa possesses the E2+/+, E+/0, and E0/– charge transitions at 0.56, 1.04, and 2.10 eV above the VBM. The incorporation of oxygen tends to cause the formation of the MnGa–VGa center, which explains a series of prior experimental observations in Mn-doped GaN. We provide a powerful tool for point defect engineering in wide band gap binary semiconductors that can be readily used to design optimal crystal growth protocols.
氮化镓是一种具有各种光电特性的不可或缺的技术材料，这主要是由于掺杂剂诱导或原生原子尺度点缺陷可产生单光子发射器、一系列发光带以及 n 型或 p 型电导率。在各种掺杂剂中，铬和锰诱导的缺陷在过去几年中尤其引人关注，因为其中一些缺陷为我们今天的发光二极管（LED）和自旋电子技术做出了贡献。然而，在铬和锰掺杂的氮化镓中，这种原子中心的性质尚待了解。对铬和锰诱导的缺陷进行全面的缺陷热力学分析对于在氮化镓晶体中进行缺陷工程至关重要，因为通过绘制缺陷稳定性与晶体生长参数的函数关系图，我们可以最大限度地提高目标点缺陷的浓度。因此，我们利用高精度交换相关混合函数，通过自证方法研究了氮化镓中铬和锰引发的缺陷，并利用 CALPHAD 方法研究了这些掺杂剂过量掺入时的相变。我们还研究了晶体生长过程中无意掺入的氧共掺物的影响。我们的分析揭示了氮化镓中与导通有关的非故意 n 型导电性的原子学原因。在掺杂铬的情况下，铬镓缺陷的形成是最主要的，在 EVBM + 2.19 eV 处会出现 E+/0 电荷转换。增加氮分压往往会提高 CrGa 的浓度。然而，在掺杂锰的情况下，根据生长条件的不同，会形成几种不同的锰相关中心，其中锰镓是最主要的。MnGa 在 VBM 以上 0.56、1.04 和 2.10 eV 处具有 E2+/+、E+/0 和 E0/- 电荷转移。氧的加入往往会导致 MnGa-VGa 中心的形成，这也解释了之前在掺锰氮化镓中所观察到的一系列现象。我们为宽带隙二元半导体中的点缺陷工程提供了一个强大的工具，可随时用于设计最佳晶体生长方案。
{"title":"Atomistic Origins of Various Luminescent Centers and n-Type Conductivity in GaN: Exploring the Point Defects Induced by Cr, Mn, and O through an Ab Initio Thermodynamic Approach","authors":"Kamil Czelej, Mubashir Mansoor, Mehmet Ali Sarsil, Mert Tas, Yahya A. Sorkhe, Mehya Mansoor, Maryam Mansoor, Bora Derin, Onur Ergen, Servet Timur, Mustafa Ürgen","doi":"10.1021/acs.chemmater.4c00178","DOIUrl":"https://doi.org/10.1021/acs.chemmater.4c00178","url":null,"abstract":"GaN is a technologically indispensable material for various optoelectronic properties, mainly due to the dopant-induced or native atomic-scale point defects that can create single photon emitters, a range of luminescence bands, and n- or p-type conductivities. Among the various dopants, chromium and manganese-induced defects have been of particular interest over the past few years, because some of them contribute to our present-day light-emitting diode (LED) and spintronic technologies. However, the nature of such atomistic centers in Cr and Mn-doped GaN is yet to be understood. A comprehensive defect thermodynamic analysis of Cr- and Mn-induced defects is essential for their engineering in GaN crystals because by mapping out the defect stabilities as a function of crystal growth parameters, we can maximize the concentration of the target point defects. We therefore investigate chromium and manganese-induced defects in GaN with <i>ab initio</i> methods using the highly accurate exchange–correlation hybrid functionals, and the phase transformations upon excess incorporation of these dopants using the CALPHAD method. We also investigate the impact of oxygen codoping that can be unintentionally incorporated during crystal growth. Our analysis sheds light on the atomistic cause of the unintentional n-type conductivity in GaN, being O<sub>N</sub>-related. In the case of Cr doping, the formation of Cr<sub>Ga</sub> defects is the most dominant, with an <i>E</i><sup>+/0</sup> charge transition at <i>E</i><sub>VBM</sub> + 2.19 eV. Increasing nitrogen partial pressure tends to enhance the concentration of Cr<sub>Ga</sub>. However, in the case of doping with Mn, several different Mn-related centers can form depending on the growth conditions, with Mn<sub>Ga</sub> being the most dominant. Mn<sub>Ga</sub> possesses the <i>E</i><sup>2+/+</sup>, <i>E</i><sup>+/0</sup>, and <i>E</i><sup>0/–</sup> charge transitions at 0.56, 1.04, and 2.10 eV above the VBM. The incorporation of oxygen tends to cause the formation of the Mn<sub>Ga</sub>–V<sub>Ga</sub> center, which explains a series of prior experimental observations in Mn-doped GaN. We provide a powerful tool for point defect engineering in wide band gap binary semiconductors that can be readily used to design optimal crystal growth protocols.","PeriodicalId":33,"journal":{"name":"Chemistry of Materials","volume":null,"pages":null},"PeriodicalIF":8.6,"publicationDate":"2024-06-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141441652","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-18DOI: 10.1021/acs.chemmater.2c00927
Zhi Lu, Shiqiang Hao, Ziliang Wang, Hyungjun Kim, Christopher Wolverton
Li-rich layered transition metal oxides (Li1+xM1–xO2 or mLi2MnO3–nLiMO2) have been widely studied as cathode materials for Li-ion batteries recently due to their enhanced capacity of larger than 250 mAh g–1. However, even the qualitative nature of the phase stability of these materials, whether they form a solid solution or are phase separated, has been the subject of intense debate. In this work, we use density functional theory calculations to investigate the phase stability of these Li-rich layered transition metal oxides (Li2MnO3–LiMO2, M = Co, Ni, Mn). We calculate the mixing enthalpy and coherency strain energy between Li2MnO3 and LiMO2 for two distinct cases: (1) mixing of M on the Li and Mn sites respectively in the transition metal layer of Li2MnO3, resulting in a solid solution with C2/m symmetry, and (2) mixing of Li and Mn on the M sites of LiMO2, resulting in a solid solution with R3̅m symmetry. We show that phase separation is energetically preferred relative to a solid solution at T = 0 K, and the coherency strain energy has little influence on phase stability. Results also display that a solid solution with R3̅m symmetry has a larger mixing enthalpy than that with C2/m symmetry at T = 0 K. Furthermore, we use the mixing enthalpies along with mean-field mixing entropies to calculate free energies and phase diagrams. At low temperature, the system exhibits phase separation between the C2/m and R3̅m phases, with appreciable solubility in each phase, and at high temperature, there is a transformation to the single-phase R3̅m solid solution. For high Li content compositions, the phase diagram shows a region of stability for the single phase C2/m solid solution. Our calculations support one possible explanation for the discrepancies between various reports of the structure of these Li-rich layered materials; the compositions and temperatures of these synthesized materials could be close to phase boundaries separating the regions of solid solution vs phase-separation. The calculated phase diagrams also indicate that the phase stability of Li-rich layered materials largely depends on the synthesis temperature, the amount of excess Li, and the combination of transition metals.
富锂层状过渡金属氧化物（Li1+xM1-xO2 或 mLi2MnO3-nLiMO2）因其容量大于 250 mAh g-1 而被广泛研究用作锂离子电池的阴极材料。然而，即使是这些材料相稳定性的定性，即它们是形成固溶体还是相分离，也一直是激烈争论的主题。在这项工作中，我们利用密度泛函理论计算来研究这些富锂层状过渡金属氧化物（Li2MnO3-LiMO2，M = Co、Ni、Mn）的相稳定性。我们计算了两种不同情况下 Li2MnO3 和 LiMO2 之间的混合焓和相干应变能：(1) Li2MnO3 过渡金属层中 Li 和 Mn 位点上的 M 分别混合，形成具有 C2/m 对称性的固溶体；(2) LiMO2 的 M 位点上 Li 和 Mn 混合，形成具有 R3̅m 对称性的固溶体。我们的研究表明，在 T = 0 K 时，相分离在能量上比固溶体优先，而相干应变能对相稳定性的影响很小。结果还显示，在 T = 0 K 时，R3̅m 对称的固溶体比 C2/m 对称的固溶体具有更大的混合焓。此外，我们还利用混合焓和平均场混合熵来计算自由能和相图。在低温下，该体系表现出 C2/m 相和 R3̅m 相之间的相分离，每种相都有明显的溶解度；在高温下，则转变为单相 R3̅m 固溶体。对于高锂离子含量成分，相图显示了单相 C2/m 固溶体的稳定区域。我们的计算支持对这些富锂层状材料结构的各种报告之间差异的一种可能解释；这些合成材料的成分和温度可能接近相界，将固溶体与相分离区域分开。计算得出的相图还表明，富锂层状材料的相稳定性在很大程度上取决于合成温度、过量锂的含量以及过渡金属的组合。
{"title":"Phase Stability of Li-rich Layered Cathodes: Insight into the Debate over Solid Solutions vs Phase Separation","authors":"Zhi Lu, Shiqiang Hao, Ziliang Wang, Hyungjun Kim, Christopher Wolverton","doi":"10.1021/acs.chemmater.2c00927","DOIUrl":"https://doi.org/10.1021/acs.chemmater.2c00927","url":null,"abstract":"Li-rich layered transition metal oxides (Li<sub>1+<i>x</i></sub>M<sub>1–<i>x</i></sub>O<sub>2</sub> or <i>m</i>Li<sub>2</sub>MnO<sub>3</sub>–<i>n</i>LiMO<sub>2</sub>) have been widely studied as cathode materials for Li-ion batteries recently due to their enhanced capacity of larger than 250 mAh g<sup>–1</sup>. However, even the qualitative nature of the phase stability of these materials, whether they form a solid solution or are phase separated, has been the subject of intense debate. In this work, we use density functional theory calculations to investigate the phase stability of these Li-rich layered transition metal oxides (Li<sub>2</sub>MnO<sub>3</sub>–LiMO<sub>2</sub>, M = Co, Ni, Mn). We calculate the mixing enthalpy and coherency strain energy between Li<sub>2</sub>MnO<sub>3</sub> and LiMO<sub>2</sub> for two distinct cases: (1) mixing of M on the Li and Mn sites respectively in the transition metal layer of Li<sub>2</sub>MnO<sub>3</sub>, resulting in a solid solution with <i>C</i>2/<i>m</i> symmetry, and (2) mixing of Li and Mn on the M sites of LiMO<sub>2</sub>, resulting in a solid solution with <i>R</i>3̅<i>m</i> symmetry. We show that phase separation is energetically preferred relative to a solid solution at T = 0 K, and the coherency strain energy has little influence on phase stability. Results also display that a solid solution with <i>R</i>3̅<i>m</i> symmetry has a larger mixing enthalpy than that with <i>C</i>2/<i>m</i> symmetry at T = 0 K. Furthermore, we use the mixing enthalpies along with mean-field mixing entropies to calculate free energies and phase diagrams. At low temperature, the system exhibits phase separation between the <i>C</i>2/<i>m</i> and <i>R</i>3̅<i>m</i> phases, with appreciable solubility in each phase, and at high temperature, there is a transformation to the single-phase <i>R</i>3̅<i>m</i> solid solution. For high Li content compositions, the phase diagram shows a region of stability for the single phase <i>C</i>2/<i>m</i> solid solution. Our calculations support one possible explanation for the discrepancies between various reports of the structure of these Li-rich layered materials; the compositions and temperatures of these synthesized materials could be close to phase boundaries separating the regions of solid solution vs phase-separation. The calculated phase diagrams also indicate that the phase stability of Li-rich layered materials largely depends on the synthesis temperature, the amount of excess Li, and the combination of transition metals.","PeriodicalId":33,"journal":{"name":"Chemistry of Materials","volume":null,"pages":null},"PeriodicalIF":8.6,"publicationDate":"2024-06-18","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141435965","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-06-18DOI: 10.1021/acs.chemmater.4c00828
Maqsuma Banoo, Arjun Kumar Sah, Raj Sekhar Roy, Pooja Bhardwaj, Digamber G. Porob, Goutam Sheet, Ujjal K. Gautam
Piezocatalytic water splitting is an emerging approach for generating green hydrogen by using noise. However, while the efficiency of hydrogen production remains limited, barely anything is known about the long-term usability of the piezocatalysts. In this study, we present single-crystalline Sr2Bi3Nb2O11Br nanoplates with precise facet control and remarkable piezoelectric properties, exhibiting a significantly enhanced piezocatalytic hydrogen production rate of 5.3 mmol/g/h without needing any expensive cocatalyst, such as Pt. Furthermore, we extend the application of these nanoplates to seawater splitting with a commendable rate retention of 4.1 mmol/g/h seawater, mimicking NaCl solution and 3.5 mmol/g/h in real, unprocessed seawater, surpassing the existing piezocatalysts operated using pure water. A key finding in this work is the fatigue-resistant nature of the Sr2Bi3Nb2O11Br nanoplates originating from the layered structure. These maintain ∼100% activity for over 150 h of continuous operation, while the existing catalysts have not been tested beyond 10–15 h, offering a sustainable approach for renewable hydrogen production.
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