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Tandem catalysis presents a promising strategy to improve the selectivity toward multicarbon products in the electrocatalytic carbon dioxide reduction reaction (CO2RR). For CO2RR, CO is a critical intermediate for producing multicarbon products. However, the management of CO localization and CO diffusion remains underexplored despite its critical role. Herein, a 3D tandem catalyst electrode with silver nanoparticles (Ag NPs) is designed to generate CO as an intermediate product within a copper (Cu) nanoneedle array. Via this nanostructured design, CO2 forms C2+ products with a high Faradaic efficiency (FEC2+) of 64% in an H‐cell and 70% in a flow cell with a current density of 350 mA cm−2. These figures‐of‐merit are currently among the top literature reports. More importantly, in situ Raman spectroscopy and finite‐element method calculations are employed to elucidate the origins of enhanced selectivity. These approaches reveal the crucial role of prolonging the CO diffusion path length for improving CO utilization during CO2 conversion with tandem catalyst systems. The favorable CO2RR FEC2+ in two distinct environments (H‐cell and flow cell) further corroborates that this effect is not limited to a particular reactor environment. Overall, this study provides new insights for designing tandem catalysts for improved CO2RR selectivity to C2+ products. [ABSTRACT FROM AUTHOR]

The electrochemical hydrogen evolution reaction (HER) that converts renewable electricity into storable hydrogen, a sustainable and clean energy carrier, provides a promising method to mitigate the energy crisis and environmental pollution. In general, noble‐metal‐based nanomaterials (including Pt, Rh, Ru, Ir, etc.) have drawn tremendous research attention in the context of the HER because of their nearly optimal bindings to hydrogen, robust stability and tunable physical/chemical properties. Particularly, carbon as a substrate not only offers a stabilizing and conductive matrix, but also impacts the electronic structure of the supported metal by interfacial interaction, necessitating a detailed understanding. To speed up the sluggish kinetics of the HER, the design and construction of efficient electrocatalysts is of crucial importance. Herein, a comprehensive review of the recent advances in carbon‐supported noble‐metal electrocatalysts is presented, focusing on their synthetic strategies, structural analyses, and applications in HER electrocatalysis. Specifically, the correlation between the electronic structure and activity is discussed. Furthermore, a perspective is offered highlighting the challenges and opportunities for development of highly efficient HER electrocatalysts, with the aim for widespread utilization of practical water electrolyzers toward green hydrogen production. [ABSTRACT FROM AUTHOR]