ACS Applied Energy Materials最新文献

Supercapacitors are energy storage devices that rapidly store and release short-term energy due to their high-power density. However, achieving both high energy density and sufficient stability is challenging. Conducting polymers like polypyrrole (PPy) show promising supercapacitive behavior but suffer from volume shrinkage during charge storage, reducing their cycling stability. Combining PPy with flexible carbon materials offers a potential solution to mitigate this issue as long as there is good contact between them. We employed the oxidative chemical vapor deposition (oCVD) method to prepare supercapacitor electrodes by depositing a submicrometer-thick layer of PPy onto carbon fabric (CF). The resulting PPy film exhibits the quinoid structure with bipolarons as dominant charge carriers, forms uniform coatings, and retains the CF’s porosity. The electrodes were characterized using electrochemical impedance spectroscopy, cyclic voltammetry, and galvanostatic charge–discharge measurements in different aqueous electrolytes (HCl, KCl, and KOH 1M), showing substantial differences in performance in the three media. Among these, KCl proved to be highly suitable for the PPy/CF electrode. Second, we investigated the effects of deposition time during oCVD on the supercapacitive performance of the electrode. Electrochemical testing revealed that extending the deposition time increases the coating thickness, electrical conductivity, and the areal capacitance of the electrode. Finally, we explored the applicability of the electrode in a symmetric supercapacitor device. The fabricated symmetric supercapacitor device exhibits ideal capacitive behavior, with a high rate capability (up to 500 mV/s) and a relatively high operational voltage (1 V).

Niobium-doped tin oxide (NTO) nanoparticles with a network structure, synthesized via flame aerosol technology, have attracted significant attention as catalyst supports in polymer electrolyte fuel cells due to their high durability and excellent cell performance. Here, we successfully synthesized NTO nanoparticles of varying sizes using spray flame techniques and systematically investigated the effects of solvent type, precursor concentration, feed rate, and oxygen dispersion gas flow rate on the crystallite size and particle size distribution of NTO nanoparticles. Increasing the mass input into the flame, through either higher precursor concentrations or higher feed rates, led to the formation of larger nanoparticles. We achieved the successful synthesis of NTO nanoparticles with controllable sizes in the range of 5 to 33 nm. The electrochemical surface area (ECSA) of Pt-loaded NTO particles with a 5 nm NTO size was 34.4 m²/g_–Pt, with Pt nanoparticles uniformly distributed across the NTO surface. The Pt/NTO sample with NTO nanoparticles of 17 nm exhibited high specific activity (j^spec_0.9 V) and mass activity (j^mass_0.9 V) at a potential of 0.9 V, with j^spec_0.9 V and j^mass_0.9 V values of 633 μA/cm² and 159 A/g, respectively.

Structural stability is critical for improving the electronic properties and charge-transfer efficiency of the catalyst, directly contributing to its enhanced electrocatalytic hydrogen evolution reaction (HER) activity. In this study, orthorhombic MoO₃ and rGO-MoO₃ catalysts were synthesized by using a straightforward hydrothermal method, and they demonstrated excellent activity for electrochemical water splitting for hydrogen generation. In this study, conventional laboratory techniques, except for Raman spectroscopy, were unable to clearly detect or differentiate the presence and impact of a very small amount (0.5%) of rGO in MoO₃. However, X-ray absorption fine structure analysis performed at the synchrotron facility provided definitive confirmation of the influence of minor rGO incorporation in this study. The analysis revealed that the incorporation of rGO suppresses lattice distortions and enhances the stability of local atomic coordination within the MoO₃ framework. The Tafel slopes for MoO₃ and rGO-MoO₃ composite nanorods are 205 and 173 mV/dec, indicating improved reaction kinetics with rGO incorporation. The estimated specific capacitance values from the linear fit of CV at different scan rates are 2.0 mF/cm² for MoO₃ and 6.7 mF/cm² for the rGO-MoO₃ composite nanorods. Therefore, this study provides valuable insights into tuning the structural properties of materials and enhancing the HER performance through the incorporation of trace amounts of carbon-based materials, effectively suppressing lattice distortions.

Aqueous flexible supercapacitors (AFSCs) are considered to be a promising power source for wearable electronics due to their fast charging, superior stability, and high safety. However, compared to conventional energy storage devices, it is still restricted by the newly emerging issue of how to balance energy density and mechanical flexibility, which is closely relative to the specific manufacturing technology and ink process. Unfortunately, to date, research on the correlation between ink composition, device structure, capacitance, and the flexibility of supercapacitors remains rare. In this work, based on the model of activated carbon (AC) and screen-printing technology, the effects of ink formulation ratios, binder types (ethyecellulose (EC), poly(vinylidene fluoride) (PVDF), carboxymethocel (CMC), and polyacrylic latex (LA133)), dimensional characteristics of carbon-based conductive agents (acetylene black, one-dimensional carbon nanotube, two-dimensional graphene), and the thickness of screen-printing layers (1–10 layers) on the electrochemical energy storage performance and mechanical flexibility of the AFSCs are systematically studied. The results indicate that relative to the excellent flexible stability of the EC binder and large capacitance of the CMC binder, the ink with LA133 as the binder exhibits both superior capacitance and flexibility. Besides, the effectiveness of carbon-based conductive agents is that graphene is better than acetylene black, and acetylene black is much better than the carbon nanotube. When the ink composition comprises 85 wt % AC, 10 wt % acetylene black, and 5 wt % LA133, and 1–3 layers of inks are printed to fabricate the AFSCs, which display the most exceptional performance, including 91.12% of capacitance maintaining after 5000 bend–fold cycles. In contrast, for an excessively thick electrode with 10 layers of ink printing, only 19.30% of the initial capacitance is retained after the same flexible test cycle. These results illustrate the critical roles of screen-printing AFSCs from the ink process in obtaining high capacitance and flexible stability.

In lithium-ion batteries, the interest in delivering a high voltage leads to the use of electrodes working outside the electrochemical stability domain of electrolytes. This is especially the case for negative electrodes. Under such conditions, the stable operation of the battery requires the buildup of a passivation layer at the electrode surface, permeable to Li ions but blocking electrolyte decomposition. The stability of this passivation layer, the so-called solid-electrolyte interphase (SEI), is instrumental for sustained battery operation. In view of enhancing the specific battery capacity, silicon-based negative electrodes are appealing but suffer from an unstable SEI. Operando infrared spectroscopy has been used for analyzing the SEI formed on methylated amorphous silicon thin-film electrodes along lithiation/delithiation cycles. It provides a quantitative measurement of the SEI thickness and, with the exception of fluorinated compounds, an assessment of its chemical composition (organic carbonate, lithium carbonate, and polycarbonate content). The methyl content of the material was varied from 0 to 10%, and the influence of boron doping was also assessed. For undoped electrodes, increasing the methyl content enhances stability during electrochemical cycling but does not reduce the SEI growth rate, at least not within the first 30 cycles. The polycarbonate growth is also insensitive to the methyl content, contrary to lithium carbonate, which grows at a lower rate upon increasing methyl content. Remarkably, the combination of boron doping and high methyl content significantly lowers the SEI growth rate, opening perspectives for electrode passivation. Moreover, the polycarbonate component grows during the first cycles and then remains approximately constant, at least for about 100 cycles. The lithium carbonate component exhibits a low growth rate at a high methyl content, accounting for the slow residual growth rate of the SEI. An electrochemical mechanism is proposed to explain the effect of doping.

An essential component of proton exchange membrane fuel cell (PEMFC) technology is the catalyst layer ionomer, serving as the binder and transport matrix responsible for the macroporous electrode structure and the regulation of proton and reactant gas supply to the catalyst interface. To improve the mass transport properties of the catalyst layer, we developed a fluorine-lean phosphonated polymer of intrinsic microporosity (pPIM). The highly kinked structure of the pPIM results in an ionomeric network with increased porosity to promote enhanced gas diffusion through the ionomer layer, while the incorporation of phosphonic acid head groups provides efficient proton conduction. Increased gas permeability of the ionomer is an important factor for effectively mitigating local transport losses that typically occur at high current densities. In situ PEMFC tests were carried out where the pPIM was utilized as the ionomer in the catalyst layer on both the anode and the cathode side. The ionomer-to-carbon (I/C) ratio was varied to evaluate its impact on the oxygen diffusion coefficient and overall fuel cell performance. A higher oxygen diffusion coefficient was achieved with the pPIM using an I/C ratio of 0.2, compared to the Nafion-based catalyst layer.

Lead-free halide double-perovskite Cs₂AgBiBr₆ nanocrystals (CABB-NC) have proven to be effective photocatalysts for the evolution of H₂ from HBr solutions. However, the photocatalytic hydrogen evolution efficacy of CABB nanocrystals is hampered by its detrimental charge recombination at the nanoscale domain. To address the challenge, Ag nanoparticles were anchored on the CABB-NC-g-C₃N₄ (AgCABBgCN) frameworks so that the plasmonic effect of silver nanoparticles (Ag NPs) could be effectively used, and synergistic photoexcitation and electron injection resulted in an enhanced hydrogen evolution performance. The AgCABBgCN system exhibited a significant photocatalytic hydrogen evolution rate (HER) of 479 μmol g^–1 h^–1, which is 10 times and 1.78 times higher than the HER of pure CABB-NC and CABB-NC/g-C₃N₄ systems, respectively. The diffuse reflectance spectra indicate an enhancement in the absorption coefficient over the entire visible range due to the surface plasmon resonance effect of the Ag NPs. The high-resolution transmission electron microscopy (HRTEM) and photoelectrochemical measurements suggest strong interfacial electron coupling between the Ag nanoparticles and CABB-NC on the g-C₃N₄ framework. The strong coupling between the CABB NCs and Ag NPs greatly promotes the generation and separation of photoinduced charge carriers while suppressing their recombination. Furthermore, the experimental results suggest a possible mechanism based on Schottky and n–n-type heterojunctions leading to synergistic photoexcitation and electron injection resulting in enhanced photocatalytic hydrogen evolution. The recyclability and reusability of the photocatalyst are demonstrated by its excellent photocatalytic cycling stability after 1 h of six repeated photocatalytic cycle experiments.

Light soaking (under continuous light exposure) significantly affects the optical and electronic properties of perovskite absorbers, affecting solar cell performance over time. This study examines the effects of light soaking on two mixed-halide, mixed-cation perovskite absorber layers, namely Cs_0.17FA_0.83Pb(I_0.9Br_0.1)₃ (CsFA) and Cs_0.05(FA_0.83MA_0.17)_0.95Pb(I_0.9Br_0.1)₃ (CsMAFA) in thin films and solar cells. Optimized CsFA and CsMAFA solar cell devices achieve PCEs of 17.1% and 18.8%, respectively. Under continuous illumination, CsMAFA devices show faster stabilization of open-circuit voltage (V_OC), indicating efficient charge separation and reduced non-radiative recombination. The steady-state and time-resolved photoluminescence (PL and TRPL) measurements suggest that MA reduces defect-induced recombination in CsMAFA, while both bulk and interfacial defects contribute in CsFA. Impedance measurements reveal better-aligned trap states in CsMAFA, facilitating faster charge collection and lower recombination losses, whereas CsFA exhibits slower response and higher recombination.

Herein, we have thoroughly investigated the potential of the van der Waals heterostructure (vdWH) MoSe₂/MoSi₂P₄ for sustainable energy applications. With a nominal lattice mismatch of ∼1.4% between the constituent monolayers, the heterostructure demonstrates dynamic stability (no imaginary phonon frequencies in the entire Brillouin zone) in all three possible stacking configurations, making it a versatile material for advanced technological applications, providing flexibility in synthesis, tunability in properties, and robustness. It exhibits identical band structures in all three stacking configurations, featuring direct band gaps of 1.02 and 1.12 eV at the Heyd–Scuseria–Ernzerhof functional level, with and without spin–orbit coupling. Additionally, it possesses a type-II band alignment to facilitate the separation of photogenerated electron–hole pairs. Our findings further reveal that the conduction band edges are optimally positioned for potential photocatalytic hydrogen production. Furthermore, the heterostructure displays a significant static dielectric constant of 7.82 as well as an optical absorption of 3.50 × 10⁵ cm^–1 in the visible region. An intense optical absorption appeared in the ultraviolet region. The determined high spectroscopic limited maximum efficiency of ∼30%, compared to those of standard high-performance thin-film absorber materials, such as CuInSe₂ (∼28%) and CdTe (∼31.5%), suggests that the studied heterostructure is a promising photovoltaic absorber material. Our findings shed light on the potential of vdWH MoSe₂/MoSi₂P₄ as a viable candidate for next-generation HER photocatalytic activity and photovoltaics.

Zero-gap CO₂-electrolyzers using a forward bias bipolar membrane (BPM) are becoming increasingly appealing, since this configuration addresses the issues of CO₂ pumping and salt precipitation observed with other approaches. However, such CO₂-electrolyzers often suffer from BPM-delamination caused by the generation of water and gaseous CO₂ at the junction between cation- and anion-exchange membranes. To circumvent this, in this study we used a rigid titanium porous transport layer (PTL) at the cathode to mechanically suppress the membrane delamination and managed to operate such cells at current densities >100 mA·cm^–2. In doing so, we compared the performance differences caused by the implementation of a catalyst-coated membrane (CCM) or a gas diffusion electrode (GDE) at the cell’s cathode. These combinations of diffusion media and catalyst layer (CL) deposition approaches result in five different configurations that systematically featured a current-driven rise in high-frequency resistance (HFR) and CO selectivity when operated at current densities <100 mA·cm^–2, whereas at current densities >100 mA·cm^–2, both HFR and CO selectivity decreased. By determining the water balance at the cathode compartment and BPM-junction, we propose that variations in membrane-CL humidification are tied to this unambiguous correlation between HFR and selectivity across all tested configurations, which we attribute to the concomitant changes in water and ion distribution (and thus pH) along this key operational interface.