EES catalysis最新文献

The electrocatalytic reduction of CO₂ offers a promising avenue for converting anthropogenic CO₂ into valuable chemical and fuel feedstocks. Copper (Cu) catalysts have shown potential in this regard, yet challenges persist in achieving high selectivity for multi-carbon (C₂₊) products. Pulsed electrolysis, employing alternating anodic and cathodic potentials (E_a/E_c) or two different cathodic potentials (E_c1/E_c2), presents a promising approach to modulate activity and selectivity. In this study, we investigate the influence of catalyst morphology and operational strategies on C₂₊ product formation using Cu nanoparticles (NPs) and CuO nanowires (NWs) in flow cells. In E_a/E_c mode, commercial Cu NPs show negligible promotion of C₂₊ selectivity while CuO NWs demonstrate enhanced C₂₊ selectivity attributed to facile oxidation/redox cycling and grain boundary formation. In contrast, E_c1/E_c2 pulsed electrolysis promotes C₂₊ yield across various catalyst morphologies by enhancing CO₂ accumulation, pH effect, and supplemental CO utilization. We further extend our investigation to membrane electrode assembly cells, highlighting the potential for scalability and commercialization. Our findings underscore the importance of catalyst morphology and operational strategies in optimizing C₂₊ product formation pulsed electrolysis, laying the groundwork for future advancements in CO₂ electroreduction technologies.

Photocatalytic selective oxidation provides a green and mild way of producing high-value added chemicals, whose conversion and selectivity are limited by complex oxidation pathways mediated by various reactive radical species. Thus, using photogenerated holes as an oxidant to directly drive these oxidation reactions could overcome the above problems, whereas the simultaneously formed electrons would cause the quenching of holes or the formation of other unfavorable reactive oxygen species that would affect the reaction efficiency. Herein, a variable-valence element doping method was proposed to realize hole-mediated photocatalytic selective oxidation. By taking Cu-doped Bi₂WO₆ as a typical prototype, we show that the doped Cu element with monovalent and divalent character can effectively trap photogenerated electrons, thereby boosting hole accumulation for selective oxidation reactions. As expected, Cu-doped Bi₂WO₆ exhibited excellent catalytic performances in oxidative coupling of benzylamines. This study provides a perspective on optimizing selective oxidation by hole regulation.

Understanding the catalytic activity of high-entropy alloys (HEAs) toward the conversion of small molecules such as carbon monoxide (CO) can provide insight into their structure–property relations. The identification of specific descriptors that govern the CO oxidation on HEAs is crucial to design new materials with customized compositions and structures. Herein, we have rationally assessed the CO oxidation mechanism on an extended AgAuCuPdPt HEA electrocatalyst under an acidic electrolyte. We compare the HEA performance with respect to platinum (Pt), palladium (Pd), and gold (Au) monometallic surfaces for CO oxidation. We also evaluated the same reaction on a binary AuPd alloy and a quaternary AuCuPdPt polycrystalline alloy with the aim of understanding the surface composition effects of the HEA. To provide insights into the descriptors controlling the CO oxidation mechanism and overpotential of the different alloy chemistry, we have combined cyclic voltammetry, surface-sensitive characterisation techniques and density functional theory (DFT) simulations. We show that silver (Ag) can improve the catalytic oxidation of CO by perturbing the *OH adsorption energy of Pd, leading to a lower onset potential. Additionally, we observed that Au segregates on the surface and that Cu is not stable at high applied potentials after CO oxidation. We highlight that HEA electrocatalysts are a valuable platform for designing more active and selective electrocatalyst surfaces.

Correction for ‘Advanced bifunctional catalyst design for rechargeable zinc–air batteries’ by Tao Wang et al., EES. Catal., 2024, https://doi.org/10.1039/d4ey00014e.

A durable, high-performing and cost-effective bi-functional catalyst toward oxygen reduction/evolution reactions (ORR/OER) is the key towards the practical application of Zn–air batteries (ZABs). Here, we report a new concept of combining pristine and carbonized MOFs for developing a bifunctional electrocatalyst for ZABs, where the pristine MOF acts as a support for the OER catalysts and the carbonized MOF acts as the ORR catalyst and enhances the electronic conductivity. By electroless NiP-plating over the surface of the Fe-containing 3D MOF (MIL-100), the catalyst shows superior activity for the OER, delivering a current density of 10 mA cm⁻² at an overpotential of 295 mV together with a low Tafel slope of 62 mV dec⁻¹. A 3D porous MOF serves as a substrate for growing NiP with maximal exposed active sites and the iron in the MOF interacts with NiP to further boost the intrinsic OER activity. Subsequently, we introduce carbonized ZIF-67 (C-ZIF-67) into NiP-MIL-100 to build a bifunctional catalyst, where C-ZIF-67 not only provides ORR catalytic activity but also creates a synergetic effect with NiP-MIL-100, and to expedite the charge/mass transfer. Using this air electrode for ZABs, an excellent bifunctionality with a small potential gap (0.78 V), a high peak power density (203 mW cm⁻²) and robust cycling over a period of 500 h were achieved.

The need to achieve net zero requires decarbonisation across all areas of our industrialised society, including the production of chemicals. One example is the production of acetonitrile, which currently relies on fossil carbon. Recently, supported Pd nanoparticles have been shown to promote the selective transformation of bio-derived ethanol to acetonitrile. Elsewhere, current research has demonstrated the importance of interstitial structures of Pd in promoting specific transformations. In this study, we demonstrate through a spatially resolved operando energy-dispersive-EXAFS (EDE) technique that selectivity to acetonitrile (up to 99%) is concurrent with the formation of a PdN_x phase. This was evidenced from the features observed in the X-ray absorption near edge structure that were validated against PdN_x samples made via known synthesis methods. Above 240 °C, the Pd nanoparticles became progressively oxidised which led to the production of unwanted byproducts, primarily CO₂. The spatially resolved analysis indicated that the Pd speciation was homogeneous across the catalyst profile throughout the series of studies performed. This work resolved the structural selectivity of Pd nanoparticles that directs ethanol ammoxidation towards acetonitrile, and provides important information on the performance descriptors required to advance this technology.

Electrocatalysts encapsulated by nanoscopic overlayers can control the rate of redox reactions at the outer surface of the overlayer or at the buried interface between the overlayer and the active catalyst, leading to complex behavior in the presence of two competing electrochemical reactions. This study investigated oxide encapsulated electrocatalysts (OECs) comprised of iridium (Ir) thin films coated with an ultrathin (2–10 nm thick) silicon oxide (SiO_x) or titanium oxide (TiO_x) overlayer. The performance of SiO_x|Ir and TiO_x|Ir thin film electrodes towards the oxygen evolution reaction (OER) and Fe(II)/Fe(III) redox reactions were evaluated. An improvement in selectivity towards the OER was observed for all OECs. Overlayer properties, namely ionic and electronic conductivity, were assessed using a combination of electroanalytical methods and molecular dynamics simulations. SiO_x and TiO_x overlayers were found to be permeable to H₂O and O₂ such that the OER can occur at the MO_x|Ir (M = Ti, Si) buried interface, which was further supported with molecular dynamics simulations of model SiO₂ coatings. In contrast, Fe(II)/Fe(III) redox reactions occur to the same degree with TiO_x overlayers having thicknesses less than 4 nm as bare electrocatalyst, while SiO_x overlayers inhibit redox reactions at all thicknesses. This observation is attributed to differences in electronic transport between the buried interface and outer overlayer surface, as measured with through-plane conductivity measurements of wetted overlayer materials. These findings reveal the influence of oxide overlayer properties on the activity and selectivity of OECs and suggest opportunities to tune these properties for a wide range of electrochemical reactions.

Scalable green hydrogen production via electrocatalytic water splitting is largely restricted by the insufficient activity and stability of oxygen evolution reaction (OER) catalysts at the anode. As a class of the most active OER catalysts in alkaline electrolyzers, the application of layered double hydroxides (LDHs) remains a main challenge owing to the unstable lattice oxygen dissolution due to the dominant lattice oxygen-involving OER mechanism during long-term operation. Herein, we found that using an epitaxial hetero-interfacing nickel hydroxide (namely Ni(OH)₂) as an electron bridge between an active FeCo LDH and Ni foam support to form an LDH*/NFO catalyst, the electronic storage capacity around the Fermi level (−0.5 to +0.5 eV, e-D_FE) sharply increases from 0.93 per cell to 1.51 per cell. Subsequently, we demonstrate that this high e-D_FE enables ceaseless and fast power injection into the kinetic process of intermediate species conversion and inhibits lattice oxygen dissolution in the active FeCo LDH. Consequently, it demonstrated a low OER overpotential of 246 mV at a current density of 100 mA cm⁻² and ultrahigh stability for up to 3500 hours with an ultraslow overpotential increase rate of 9.4 × 10⁻³ mV h⁻¹. Therefore, we developed an epitaxial hetero-interfacial electron bridging strategy to synchronize the activity and stability of available catalysts for scalable green hydrogen production via electrocatalytic water splitting.

The conversion of ethane to ethylene is crucial for deriving platform chemicals from non-petroleum feedstock. However, it currently relies on steam cracking technology, which involves high temperatures and large reactors. The catalytic dehydrogenation of ethane (EDH) could resolve these issues, but its efficiency is often limited due to thermodynamics, leading to low conversion and coke formation. These challenges make it difficult for catalytic EDH to compete economically with steam cracking. Recent studies show that rational design of catalysts, such as fixing metal nanoclusters within zeolite micropores or isolated metal sites on the zeolite framework, can enhance catalytic performances. These designs lower energy barriers for carbon–hydrogen bond activation, hinder deep dehydrogenation to coke, and provide sinter-resistant metal sites for durability. This review discusses the pivotal role of zeolite structures in catalysis and sums up the principles of catalyst design for efficient non-oxidative EDH. It aims to help in the development of more efficient zeolite catalysts and enhance the viability of catalytic EDH for potential industrialization.

Renewable-powered CO₂ electrolysis (CO₂E) is a promising strategy to reduce greenhouse gas emissions by transforming CO₂ into valuable feedstocks. While recent studies in this field have focused on developing efficient catalyst materials or electrolyzer engineering, the operating temperature's effect has not been systematically examined for zero-gap electrolyzers. To examine the effects of operating temperature, a systematic investigation was conducted using zero-gap (MEA) Cu-based GDEs across a range from room temperature to 80 °C. Our results indicate that increasing the temperature improves CO₂ mass transport, ionic conductivity, and water management, allowing for high catalytic activity toward CO₂E. At operating temperatures greater than 50 °C, selectivity shifted substantially towards CO, with surface enhanced infrared absorption spectroscopy (SEIRAS) showing a concomitant decrease in surface CO coverage at and above this temperature. As commercial electrolyzers will operate at elevated temperatures due to ohmic heating, they may produce a significantly different product distribution than the room-temperature electrolysis prevalent in the literature. Experiments at elevated temperatures demonstrated improved results for CO₂E with industrially relevant current densities (150 mA cm⁻²) over an extended operational period (>200 hours). Additionally, we found that the heating method strongly affects product selectivity and the electrolyzer's performance, emphasizing the need to ensure proper heating while working under these reaction systems.