EES catalysis最新文献

Photoelectrocatalytic (PEC) water splitting offers a sustainable pathway for clean H₂ production, and its integration with biomass valorization further enhances eco-economic efficiency. In this study, a BiVO₄ catalyst with an optimized oxygen vacancy (Ov-BVO) concentration was grown on a SnO₂ skeleton, achieving efficient PEC glycerol oxidation to selectively produce dihydroxyacetone (DHA) and H₂ under neutral conditions. By incorporating Ov-BVO with SnO₂, the light-harvesting and photo-induced carrier transfer efficiencies were significantly improved. Ov played a crucial role in selectively absorbing and activating the secondary –OH group of glycerol molecules, as revealed by theoretical and experimental studies. However, excessive Ov induced carrier recombination, underscoring the need for an optimal Ov concentration, which was achieved by tailoring heat treatment conditions. The SnO₂/BVO-400 catalyst demonstrated a trade-off between the prolonged carrier lifetime and efficient reactant adsorption, exhibiting a PEC DHA productivity of 144 mmol m⁻² h⁻¹ with 26.5% selectivity, alongside H₂ generation (1850 mmol m⁻² h⁻¹). This work lays the groundwork to achieve value-added chemical fabrication through neutral PEC glycerol reforming and the potential scale-up of this sustainable technology.

We study the selective catalytic hydrogenation of C₂H₂, the main product from non-oxidative CH₄ coupling in gas-phase plasmas, to C₂H₄, a cornerstone of the global chemical industry, by experiments and temperature-dependent micro-kinetic modelling. The model is validated against new experimental data from a nanosecond pulsed plasma reactor integrated with a downstream catalytic bed consisting of Pd/Al₂O₃. We explore the effects of varying Pd loadings (0.1, 0.5, and 1 wt%) on the catalyst activity and the C₂H₄/C₂H₆ product distribution. Consistent with the experimental data, our surface micro-kinetic model shows that while higher Pd loadings lower the catalyst activation temperature for C₂H₂ conversion, they also induce over-hydrogenation to C₂H₆ at lower temperatures and increase oligomerisation in the experiments, which are detrimental to the C₂H₄ yield. The model also elucidates reaction mechanisms and pathways across different temperature regimes, expanding our understanding of the hydrogenation process beyond the experimental range. Besides highlighting the importance of optimising the metal loading to balance C₂H₄ and C₂H₆ selectivity, our findings demonstrate the effective implementation of post-plasma catalysis using a simple catalyst bed heated by hot gas from the plasma region. This study opens possibilities for testing different plasma sources, catalysts, gas flow magnitude and patterns, and catalyst bed-to-plasma distances.

Photoelectrochemical (PEC) CO₂ reduction (CO₂R) on semiconductors provides a promising route to convert CO₂ to fuels and chemicals. However, most semiconductors are not stable under CO₂R conditions in aqueous media and require additional protection layers for long-term durability. To identify materials that would be stable and yield CO₂R products in aqueous conditions, we investigated bare Cu(In,Ga)S₂ (CIGS) thin films. We synthesized CIGS thin films by sulfurizing a sputtered Cu–In–Ga metal stack. The as-synthesized CIGS thin films are Cu-deficient and have a high enough bandgap (1.7 eV) suitable to perform CO₂R. The bare CIGS photocathodes had faradaic yields of 14% for HCOO⁻ and 30% for CO in 0.1 M KHCO₃ electrolyte without the use of any co-catalysts under 1 sun illumination at an applied bias of −0.4 V vs. RHE and operated stably for 80 min. Operando Raman spectroscopy under CO₂R conditions showed that the dominant A₁ mode of CIGS was unaffected during operation. Post-mortem X-ray photoelectron spectroscopy (XPS) and X-ray absorption spectroscopy (XAS) analysis suggests that the CO₂R stability could be related to self-protection caused by the in situ formation of oxides/hydroxides of Ga and In during operation. Density functional theory (DFT) calculations also reveal that Ga and In are the preferential sites for the adsorption of CO₂R products, particularly HCOO⁻. These results show that CIGS is a promising semiconductor material for performing direct semiconductor/electrolyte reactions in aqueous media for the PEC CO₂R.

Electrochemical CO₂ reduction (CO₂R) in conventional systems typically generates highly diluted product output streams. This necessitates energy intensive and costly product separation, which potentially decreases the feasibility and economic viability of the process. Here, we describe the design and fabrication of a reversed gas diffusion electrode, which makes use of electrolyte pressure to channel products toward a collection chamber. Importantly, this strategy successfully excludes CO₂ and permits gas products to be siphoned off at high purity. We further show that the electrolyte pressure and gas diffusion layer pore size are the key factors which govern the product collection efficiency. Using a nanoporous Au catalyst, we showcase the continuous production of high purity syngas over an extended 76 h period, operating at a full-cell energy efficiency of 37%. Importantly, we also demonstrate that this system is oxygen-tolerant, with no parasitic loss of current towards the oxygen reduction reaction even with a 95% CO₂ + 5% O₂ gas feed. Taken together, our results introduce a new design approach for CO₂R electrolyzer systems.

Herein, we demonstrate the unique neighboring effect of single-cobalt active sites anchored on BiOCl nanosheets with high CO₂ photoreduction performances by combining in situ X-ray photoelectron with in situ infrared spectroscopy. More specifically, single-atom Co sites demonstrate an exceptional electron-enriched feature from adjacent Bi atoms, which facilitates the formation of *CO₂–Co and *H₂O–Bi species, respectively. Under light irradiation, the photoinduced electron transfer from adjacent Bi atoms to single Co active sites is favorable for the formation *COOH and *CO intermediates, accompanied by the oxidation of H₂O molecules into *OH and *OOH species on Bi sites. As a result, these dynamic electronic interactions between single-atom Co and adjacent Bi sites are responsible for a record CO evolution activity of 172.6 μmol g⁻¹ h⁻¹ under sunlight illumination, which exceeds that of pristine BiOCl by nearly one order of magnitude. These findings provide a fundamental understanding of the intrinsic neighboring effect between single-atom sites and adjacent atoms, which should be crucial and essential for the development of high-performance single-atom catalysts.

Crystalline silicon (c-Si) is a promising material for photoelectrochemical (PEC) ammonia (NH₃) production from nitrate (NO₃⁻) reduction owing to its appropriate band gap and optimal charge-transport properties. However, c-Si is not stable in aqueous solutions, causing the detachment of catalysts from the c-Si photoelectrode and resulting in a dramatic decrease in the performance. Furthermore, electrocatalysts on c-Si block light, therby reducing the PEC NH₃-production efficiency. Herein, we stabilized and increased the efficiency of the c-Si photocathode by TiO₂ deposition and loaded an optimized amount of Au using an e-beam patterning, respectively. We found that TiO₂ not only protects the c-Si photoelectrode from the electrolyte but also promotes strong bonding between Au and the c-Si photoelectrode. Notably, TiO₂ showed a synergistic effect with the Au electrocatalyst in increasing the faradaic efficiency (FE) of NO₃⁻ reduction for NH₃ production, which was further confirmed by density functional theory calculations. Overall, the Au-loaded TiO₂-protected c-Si photoelectrode showed a stable and record-high NH₃-production rate of 1590 ± 40 μg_NH3 cm⁻² h⁻¹ with an FE of 83.4% ± 5.6% at −0.35 V vs. the reversible hydrogen electrode.

Upgrading anthropogenic CO₂ from concentrated point sources or directly from the atmosphere is a valuable approach in closing the carbon cycle. Existing processes capture the CO₂, concentrate it into pure gas streams, transport it, and then convert it into fuels and chemicals in a separate process plant. This sequential approach results in higher energy and operating costs which can be reduced by integrating the capture and conversion steps to directly reduce the captured CO₂-bound adduct to value-added products. The direct reduction of the captured CO₂-bound adduct is called the captured-CO₂ reduction reaction (c-CO₂RR). Understanding of c-CO₂RR has been obscured by the higher intrinsic complexity of the system. The CO₂ capture media is a complex space of several buffer reactions that allow the co-existence of different carbon species in solution depending on CO₂ loading, temperature, pressure, and pH. In order to design improved capture agents and catalysts for integrated CO₂ capture and conversion, it is essential to identify the carbon source and the primary factors influencing product formation on a c-CO₂RR catalyst. This review delineates the strategies to determine the active carbon species for integrated CO₂ capture and conversion systems. Furthermore, it summarizes the fundamental applications of mass transport, thermodynamics, and kinetics across various c-CO₂RR scenarios.

Ammonia (NH₃) is a vital chemical feedstock and a carbon-free energy source. The reduction of nitrate (NO₃⁻) from environmental pollutants is a sustainable method for NH₃ production compared with the industrially intensive Haber–Bosch method, which can mitigate energy and environmental concerns. However, due to the involvement of multi-electron transfer-proton coupling processes, the NO₃⁻ reduction reaction (NO₃RR) exhibits sluggish kinetics and significant side reactions. This review provides a comprehensive summary of recent research progress in facilitating NO₃RRs using a built-in electric field and external stimuli. The paper commences by introducing the mechanisms and challenges of the NO₃RR, subsequently focusing on strategies for built-in electric field/external stimuli-assisted catalytic reactions. The internal electric field can be triggered by constructing a Mott–Schottky heterojunction and a semiconductor–semiconductor heterojunction, adjusting the coordination environment of active sites, and regulating the electrical double layer, while the external stimuli include optical, stress, and thermal stimuli. This review focuses on the activation and adsorption processes of reactants and intermediates by a built-in electric field/external stimuli, and their influence on the thermodynamics and kinetics of reactions. Finally, we summarize the strategies for built-in electric field/external stimuli-assisted NO₃RRs, highlight the challenges of achieving high activity and selectivity in NH₃ production, and provide clear guidance for future research.

H₂ production from air holds great promise as a sustainable method for green energy harvesting. However, its widespread adoption faces challenges in realizing mobile, distributed, community-managed, off-grid in situ H₂ production systems. Here, we report a bilayer nanofibrillated cellulose composite gel incorporating lithium chloride hygroscopic salt and a supported SrTiO₃:Al photocatalyst (denoted as NLS), designed specifically for in situ photocatalytic splitting of atmospheric water to produce H₂, using only naturally occurring moisture and sunlight. The NLS gel features a self-supply of atmospheric water, spectral splitting for efficient solar energy delivery and complementary utilization, instantaneous H₂ evolution, and stable catalyst immobilization. As a result, the NLS bilayer gel successfully achieves in situ H₂ production in full-range-humidity environments, demonstrating a hygroscopicity of 4.26 g_H2O g_sorbent⁻¹ and an H₂ production activity of 65.45 μmol h⁻¹ in a 90% relative humidity environment, achieving a solar-to-hydrogen efficiency of up to 0.3%. This work represents a promising step towards realizing in situ H₂ production from air across varying humidity levels, independent of geographical constraints.

Electrochemical CO₂ reduction offers a promising method of converting renewable electrical energy into valuable hydrocarbon compounds vital to hard-to-abate sectors. Significant progress has been made on the lab scale, but scale-up demonstrations remain limited. Because of the low energy efficiency of CO₂ reduction, we suspect that significant thermal gradients may develop in industrially relevant dimensions. We describe here a model prediction for non-isothermal behavior beyond the typical 1D models to illustrate the severity of heating at larger scales. We develop a 2D model for two membrane electrode assembly (MEA) CO₂ electrolyzers; a liquid anolyte fed MEA (exchange MEA) and a fully gas fed configuration (full MEA). Our results indicate that full MEA configurations exhibit very poor electrochemical performance at moderately larger scales due to non-isothermal effects. Heating results in severe membrane dehydration, which induces large Ohmic losses in the membrane, resulting in a sharp decline in the current density along the flow direction. In contrast, the anolyte employed in the exchange MEA configuration is effective in preventing large thermal gradients. Membrane dehydration is not a problem for the exchange MEA configuration, leading to a nearly constant current density over the entire length of the modeled domain, and indicating that exchange MEA configurations are well suited for scale-up. Our results additionally indicate that a balance between faster kinetics, higher ionic conductivity, smaller pH gradients and lower CO₂ solubility causes an optimum operating temperature between 60 and 70 °C.