Bimetallic Gold-Silver Nanostructures Drive Low Overpotentials for Electrochemical Carbon Dioxide Reduction

Collaborative rapid reduction promoted synthesis of highly alloyed AuAg aerogels for selective CO2 reduction to CO

Developing electrocatalysts combining both high selectivity and durability toward CO2 electrochemical reduction reaction (CO2RR) to high value products is of great importance but challenging. The favorable influences of high alloying degree on electrocatalytic performance have been frequently revealed in various electrochemical energy conversions whereas rarely studied in CO2RR. Herein, we propose a facile "one-pot galvanic replacement reaction-chemical reduction collaborative rapid reduction strategy" (GRR-CR) for the synthesis of highly alloyed Au50Ag50 aerogel (Au50Ag50-① AG) that exhibits high CO selectivity and high stability in CO2RR. During the synthesis, galvanic replacement reaction (GRR) between HAuCl4 and Ag and the reduction of metal ions by NaBH4 proceed simultaneously. The large number of vacancies generated during GRR facilitate the mutual diffusion and alloying of Au and Ag atoms, leading to high alloying degree in Au50Ag50-① AG. Compared with the Au50Ag50 aerogel obtained by two-step gelation method (Au50Ag50-② AG) with certain micro-phase separation, the Au50Ag50-① AG showed much better CO2RR performance. Specifically, at -0.7 V vs. RHE, the FECO of Au50Ag50-① AG achieve 97.8 %, much higher than 61.7 % for the Au50Ag50-② AG. Besides, the intrinsic activity JCO ECSA of Au50Ag50-① AG is 4.3 times that of the Au50Ag50-② AG, and the Au50Ag50-① AG shows good durability with the FECO remains 87.3 % after 18 h. Theoretical simulation proved that the increase of alloying degree is conducive to reducing the energy barrier of CO2-CO rate-determining step, promoting the formation of *COOH and *CO, and improves the overall performance of CO2RR. This work sheds promising light on the design of CO2RR electrocatalyst of both high selectivity and stability especially toward CO product.

Non-isothermal CO2 electrolysis enables simultaneous enhanced electrochemical and anti-precipitation performance

Electrochemical conversion of CO2 into fuels represents an important pathway for addressing the challenges of climate change and energy storage. However, large-scale applications remain hindered by the instability and inefficiency of CO2 reduction systems, particularly under highly alkaline electrolytes and high current densities. One primary obstacle is the cathodic salt precipitation, which hinders mass transfer and blocks active sites limiting the lifespan of these systems. Here, we present a non-isothermal strategy that leverages a thermal gradient across the membrane electrode assembly to enhance electrochemical performance and suppress salt precipitation. By maintaining a cooler cathode and warmer anode, we exploit the Soret effect to drive cations away from the cathode, mitigating salting-out while boosting anodic activity and cathodic CO2 solubility. The non-isothermal case has demonstrated over 200 h of stable operation at 100 mA cm-2 under highly alkaline conditions, outperforming conventional isothermal systems. Techno-economic analysis reveals reductions in CO2-to-CO production costs, supporting the scalability of this strategy. These findings enable the practical deployment of stable, high-efficiency CO2 electrolysis systems.

Bimetallic effects in carbon dioxide electroreduction

As a clean and sustainable technology, electrocatalytic carbon dioxide reduction reaction (ECO2RR) occupies a central position in the global energy transformation and climate change strategy. Compared with single metallic catalysts, bimetallic catalysts have many advantages, such as the synergistic effect between bimetals, enhanced CO2 adsorption capacity, and lower reaction energy barriers, which make them widely used in the CO2RR for the generation of multi-carbon products. This review systematically summarizes the latest advances in bimetallic effects for the CO2RR. In this paper, we start with a classified introduction on the CO2RR mechanisms, followed by a comprehensive discussion of the structure-activity relationships of various bimetallic catalysts, including regulation of metal centers, regulation of the distance between metal sites, regulation of the coordination environment, interface engineering, and strain engineering. Next, we showcase the advantages of bimetallic catalysts in the CO2RR. Then, the research progress of typical bimetallic catalysts for the ECO2RR is discussed, including diatomic catalysts, bimetallic alloys, bimetallic MOFs and bimetallic COFs. Finally, we summarize the challenges faced today from the five aspects of product selectivity, catalyst stability, product purification, theoretical simulations and in situ characterization techniques and put forward the research direction to promote the industrialization process of CO2RR.

Single Entity Electrocatalysis

Making a measurement over millions of nanoparticles or exposed crystal facets seldom reports on reactivity of a single nanoparticle or facet, which may depart drastically from ensemble measurements. Within the past 30 years, science has moved toward studying the reactivity of single atoms, molecules, and nanoparticles, one at a time. This shift has been fueled by the realization that everything changes at the nanoscale, especially important industrially relevant properties like those important to electrocatalysis. Studying single nanoscale entities, however, is not trivial and has required the development of new measurement tools. This review explores a tale of the clever use of old and new measurement tools to study electrocatalysis at the single entity level. We explore in detail the complex interrelationship between measurement method, electrocatalytic material, and reaction of interest (e.g., carbon dioxide reduction, oxygen reduction, hydrazine oxidation, etc.). We end with our perspective on the future of single entity electrocatalysis with a key focus on what types of measurements present the greatest opportunity for fundamental discovery.

From Biomimicking to Bioinspired Design of Electrocatalysts for CO2 Reduction to C1 Products

The electrochemical reduction of CO2 (CO2 RR) is a promising approach to maintain a carbon cycle balance and produce value-added chemicals. However, CO2 RR technology is far from mature, since the conventional CO2 RR electrocatalysts suffer from low activity (leading to currents <10 mA cm-2 in an H-cell), stability (<120 h), and selectivity. Hence, they cannot meet the requirements for commercial applications (>200 mA cm-2 , >8000 h, >90 % selectivity). Significant improvements are possible by taking inspiration from nature, considering biological organisms that efficiently catalyze the CO2 to various products. In this minireview, we present recent examples of enzyme-inspired and enzyme-mimicking CO2 RR electrocatalysts enabling the production of C1 products with high faradaic efficiency (FE). At present, these designs do not typically follow a methodical approach, but rather focus on isolated features of biological systems. To achieve disruptive change, we advocate a systematic design methodology that leverages fundamental mechanisms associated with desired properties in nature and adapts them to the context of engineering applications.

Disproportional surface segregation in ligand-free gold-silver alloy solid solution nanoparticles, and its implication for catalysis and biomedicine

Catalytic activity and toxicity of mixed-metal nanoparticles have been shown to correlate and are known to be dependent on surface composition. The surface chemistry of the fully inorganic, ligand-free silver-gold alloy nanoparticle molar fraction series, is highly interesting for applications in heterogeneous catalysis, which is determined by active surface sites which are also relevant for understanding their dissolution behavior in biomedically-relevant ion-release scenarios. However, such information has never been systematically obtained for colloidal nanoparticles without organic surface ligands and has to date, not been analyzed in a surface-normalized manner to exclude density effects. For this, we used detailed electrochemical measurements based on cyclic voltammetry to systematically analyze the redox chemistry of particle-surface-normalized gold-silver alloy nanoparticles with varying gold molar fractions. The study addressed a broad range of gold molar fractions (Ag₉₀Au₁₀, Ag₈₀Au₂₀, Ag₇₀Au₃₀, Ag₅₀Au₅₀, Ag₄₀Au₆₀, and Ag₂₀Au₈₀) as well as monometallic Ag and Au nanoparticle controls. Oxygen reduction reaction (ORR) measurements in O₂ saturated 0.1 M KOH revealed a linear reduction of the overpotential with increasing gold content on the surface, probably attributed to the higher ORR activity of gold over silver, verified by monometallic Ag and Au controls. These findings were complemented by detailed XPS studies revealing an accumulation of the minor constituent of the alloy on the surface, e.g., silver surface enrichment in gold-rich particles. Furthermore, highly oxidized Ag surface site enrichment was detected after the ORR reaction, most pronounced in gold-rich alloys. Further, detailed CV studies at acidic pH, analyzing the position, onset potential, and peak integrals of silver oxidation and silver reduction peaks revealed particularly low reactivity and high chemical stability of the equimolar Au₅₀Ag₅₀ composition, a phenomenon attributed to the outstanding thermodynamic, entropically driven, stabilization arising at this composition.

Laser-ablation assisted strain engineering of gold nanoparticles for selective electrochemical CO2 reduction

Strain engineering can endow versatile functions, such as refining d-band center and inducing lattice mismatch, on catalysts for a specific reaction. To this end, effective strain engineering for introducing strain on the catalyst is highly sought in various catalytic applications. Herein, a facile laser ablation in liquid (LAL) strategy is adopted to synthesize gold nanoparticles (Au NPs) with rich compressive strain (Au-LAL) for electrochemical CO₂ reduction. It is demonstrated that the rich compressive strain can greatly promote the electrochemical CO₂ reduction performance of Au, achieving a CO partial current density of 24.9 mA cm^-2 and a maximum CO faradaic efficiency of 97% at -0.9 V for Au-LAL, while it is only 2.77 mA cm^-2 and 16.2% for regular Au nanoparticles (Au-A). As revealed by the in situ Raman characterization and density functional theory calculations, the presence of compressive strain can induce a unique electronic structure change in Au NPs, significantly up-shifting the d-band center of Au. Such a phenomenon can greatly enhance the adsorption strength of Au NPs toward the key intermediate of CO₂ reduction (i.e., *COOH). More interestingly, we demonstrate that, an important industrial chemical feedstock, syngas, can be obtained by simply mixing Au-LAL with Au-A in a suitable ratio. This work provides a promising method for introducing strain in metal NPs and demonstrates the important role of strain in tuning the performance and selectivity of catalysts.

Engineering the degree of concavity of one-dimensional Au-Cu alloy nanorods with partial intermetallic compounds by facile wet chemical synthesis

Finely modulating the morphology of bimetallic nanomaterials plays a vital role in enhancing their catalytic activities. Among the various morphologies, concave structures have received considerable attention due to the three advantageous features of high-index facets, high surface areas, and high curvatures, which contribute greatly to enhancing the catalytic performance. However, concave morphologies are not the products generated from thermodynamically controlled growth with minimized surface energy. Additionally, most nanocrystals with concave shapes are currently in the state of mono-metals or alloys with disordered arrangements of atoms. The synthesis of alloy structures with ordered atom arrangements, intermetallic compounds, which tend to display superior catalytic performance on account of their optimal geometric and electronic effects, has rarely been reported as high-temperature annealing is usually needed, which constrains the modulation of morphology and surface structure. In this work, concave one-dimensional Au-Cu nanorods with a partially ordered intermetallic structure were synthesized via a facile wet chemical method. By simply adjusting the reaction kinetics via the concentrations of the corresponding metal precursors, the degree of concavity of the one-dimensional Au-Cu nanorods could be regulated. In both the p-nitrophenol reduction and CO₂ electro-reduction reactions, the concave-shaped Au-Cu nanorods demonstrated superior catalytic activity compared to corresponding non-concave samples with the same structure due to the morphological advantages provided by the concave structure.