A General Synthetic Approach for Integrated Nanocatalysts of Metal-Silica@ZIFs

Integration of different nanocomponents into a greater assemblage or object for applications poses a significant challenge to materials chemists. At present, it still remains extremely difficult to achieve high monodispersivity for such assembled products. To gain better synthetic controllability, ideally, an integration of this type should be done in a stepwise manner. Herein, we report a versatile stepwise approach for preparation of integrated nanocatalysts of metal-<i>m</i>SiO₂@ZIFs (metal = Pt, Pd, Ru, Ag, and Pt₅₃Ru₄₇; <i>m</i>SiO₂ = mesoporous silica; and ZIFs = ZIF-8 and ZIF-67). Starting with uniform solid Stöber silica spheres in submicrometer scale, mesoporous channels with desired length and diameter can be created for silica which serves as a support. With measurements of amino-modification of mesopores and selection of metal precursors applied, subsequently, ultrafine metal nanoparticles (2–5 nm) can be deposited evenly onto the inner walls of silica channels. Resultant metal-<i>m</i>SiO₂ spheres are then modified by a layer of anionic polymer which imparts negative charges around and facilitates coating of ZIF-8 shell and thus formation of metal-<i>m</i>SiO₂@ZIF-8. Through coordination interaction between polyvinylpyrrolidone (PVP; as surfactant molecules) and unsaturated Zn²⁺ ions exposed on the ZIF-8 shell, uniform metal-<i>m</i>SiO₂@ZIF-8 spheres with desired shape and size can be obtained and simultaneously well-dispersed. Fundamental study and optimization are also carried out, aiming at a greater generality of this synthetic approach. The workability of these catalysts is demonstrated with hydrogenation of different alkenes using as-produced Pd-<i>m</i>SiO₂@ZIF-8 catalyst. Indeed, reactant-selective hydrogenation is achieved based on different interactions of the alkene molecules with the shell structure of ZIF-8, possibly influencing the flexible gate opening of ZIF-8

Tunable Product Selectivity in Electrochemical CO₂ Reduction on Well-Mixed Ni–Cu Alloys

Electrochemical reduction of CO2 on copper-based catalysts has become a promising strategy to mitigate greenhouse gas emissions and gain valuable chemicals and fuels. Unfortunately, however, the generally low product selectivity of the process decreases the industrial competitiveness compared to the established large-scale chemical processes. Here, we present random solid solution Cu1–xNix alloy catalysts that, due to their full miscibility, enable a systematic modulation of adsorption energies. In particular, we find that these catalysts lead to an increase of hydrogen evolution with the Ni content, which correlates with a significant increase of the selectivity for methane formation relative to C2 products such as ethylene and ethanol. From experimental and theoretical insights, we find the increased hydrogen atom coverage to facilitate Langmuir–Hinshelwood-like hydrogenation of surface intermediates, giving an impressive almost 2 orders of magnitude increase in the CH4 to C2H4 + C2H5OH selectivity on Cu0.87Ni0.13 at −300 mA cm–2. This study provides important insights and design concepts for the tunability of product selectivity for electrochemical CO2 reduction that will help to pave the way toward industrially competitive electrocatalyst materials

Pitfalls and Protocols: Evaluating Catalysts for CO₂ Reduction in Electrolyzers Based on Gas Diffusion Electrodes

The evaluation of catalysts on gas diffusion electrodes (GDEs) have propelled the progress of electrochemical CO2 reduction reaction (CO2RR) at industry-relevant activities. However, high experimental complexities exist in GDE-based flow electrolyzers, whereby various experimental factors can influence the evaluation of catalytic CO2RR performances. Not accounting for these experimental factors could result in inconsistent conclusions and thus hinder rational catalyst developments. This Perspective highlights a range of experimental factors that can affect the performance metrics for electrocatalysts. Specifically, the product faradaic efficiency can be influenced by the overestimation of the effluent gas flow rate, unaccounted losses of products, and unintended alteration of microenvironments. In addition, cathodic voltage can be inaccurately determined due to the unaccounted dynamic changes in uncompensated resistance. By raising awareness of these potential pitfalls and establishing appropriate protocols, we foresee a more meaningful benchmarking of catalytic performances across the literature

Enhancing Glycerol Conversion and Selectivity toward Glycolic Acid via Precise Nanostructuring of Electrocatalysts

The glycerol electro-oxidation reaction (GEOR) can economically convert glycerol, a byproduct of biodiesel production, to glycolic acid. Herein, nanostructured Au catalysts were fabricated on a Si substrate by the electrochemical reduction of anodic-treated (RA-treatment) Au films, which tuned the surface area from 1 to 16 cm2. Treatment of 0.1 M glycerol at 1.0 V (vs RHE) for 2 h in 1 M KOH solution afforded a glycerol conversion and glycolic acid selectivity of 50.9 and 47%, respectively. The RA-Au catalyst selectively afforded glycolic acid from glycerol due to the enhanced facet-dependent OH adsorption, especially at the (100) and (110) sites, as well as the increased surface area. RA treatment of a Au-coated Ni foam further enhanced the GEOR performance, affording 68.7% glycerol conversion and 41.2% glycolic acid selectivity at 1.0 V (vs RHE) within 2 h by providing more active sites

Over a 15.9% Solar-to-CO Conversion from Dilute CO₂ Streams Catalyzed by Gold Nanoclusters Exhibiting a High CO₂ Binding Affinity

Development of efficient and selective electrocatalysts is a key challenge to achieve an industry-relevant electrochemical CO2 reduction reaction (CO2RR) to produce commodity chemicals. Here, we report that Au25 clusters with Au-thiolate staple motifs can initiate electrocatalytic reduction of CO2 to CO with nearly zero energy loss and achieve a high CO2RR current density of 540 mA cm–2 in a gas-phase reactor. Electrochemical kinetic investigations revealed that the high CO2RR activity of the Au25 originates from the strong CO2 binding affinity, leading to high CO2 electrolysis performance in both concentrated and dilute CO2 streams. Finally, we demonstrated an 18.0% solar-to-CO conversion efficiency using a Au25 electrolyzer powered by a Ga0.5In0.5P/GaAs photovoltaic cell. The electrolyzer also showed 15.9% efficiency and a 5.2% solar-driven single-path CO2 conversion rate in a 10% CO2 gas stream, the CO2 concentration in a typical flue gas

Trace-Level Cobalt Dopants Enhance CO₂ Electroreduction and Ethylene Formation on Copper

The development of Cu-based catalysts for electrochemical CO2 reduction reaction (CO2RR) with stronger CO-binding elements had been unsuccessful in improving multicarbon production from the CO2RR due to CO-poisoning. Here, we discover that trace doping levels of Co atoms in Cu, termed CoCu single-atom alloy (SAA), achieve up to twice the formation rate of CO as compared to bare Cu and further demonstrate a high jC2H4 of 282 mA cm–2 at −1.01 VRHE in a neutral electrolyte. From DFT calculations, Cu sites neighboring CO-poisoned Co atomic sites accelerate CO2-to-CO conversion and enhance the coverage of *CO intermediates required for the formation of multicarbon products. Furthermore, CoCu SAA also exhibits active sites that favor the deoxygenation of *HOCCH, which increases the selectivity toward ethylene over ethanol. Ultimately, CoCu SAA can simultaneously boost the formation of *CO intermediates and modulate the selectivity toward ethylene, resulting in one of the highest ethylene yields of 15.6%