Electrochemical reduction of CO2 could mitigate environmental problems originating from CO2 emission. Although grain boundaries (GBs) have been tailored to tune binding energies of reaction intermediates and consequently accelerate the CO2 reduction reaction (CO2RR), it is challenging to exclusively clarify the correlation between GBs and enhanced reactivity in nanostructured materials with small dimension (<10 nm). Now, sub‐2 nm SnO2 quantum wires (QWs) composed of individual quantum dots (QDs) and numerous GBs on the surface were synthesized and examined for CO2RR toward HCOOH formation. In contrast to SnO2 nanoparticles (NPs) with a larger electrochemically active surface area (ECSA), the ultrathin SnO2 QWs with exposed GBs show enhanced current density (j), an improved Faradaic efficiency (FE) of over 80 % for HCOOH and ca. 90 % for C1 products as well as energy efficiency (EE) of over 50 % in a wide potential window; maximum values of FE (87.3 %) and EE (52.7 %) are achieved.

Bi2O3 nanosheets were grown on a conductive multiple channel carbon matrix (MCCM) for CO2RR. The obtained electrocatalyst shows a desirable partial current density of ca. 17.7 mA cm−2 at a moderate overpotential, and it is highly selective towards HCOOH formation with Faradaic efficiency approaching 90 % in a wide potential window and its maximum value of 93.8 % at −1.256 V. It also exhibits a maximum energy efficiency of 55.3 % at an overpotential of 0.846 V and long‐term stability of 12 h with negligible degradation. The superior performance is attributed to the synergistic contribution of the interwoven MCCM and the hierarchical Bi2O3 nanosheets, where the MCCM provides an accelerated electron transfer, increased CO2 adsorption, and a high ratio of pyrrolic‐N and pyridinic‐N, while ultrathin Bi2O3 nanosheets offer abundant active sites, lowered contact resistance and work function as well as a shortened diffusion pathway for electrolyte.

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The renewable-energy-powered electrochemical CO 2 reduction reaction (CO 2 RR) provides an attractive strategy to simultaneously address the energy storage and environmental issues through the synthesis of carbon-neutral fuels. This study unravels structure sensitivity of ultrasmall Ag nanocubes with lengths below 25 and 70 nm (L25-and L70-Ag-NCs) enclosed completely by the (100) facet toward an efficient CO 2 RR to CO. The ultrasmall L25-Ag-NCs deliver a remarkably larger current density, a significantly higher Faraday efficiency (FE) of near-unity, and a comparably higher energy efficiency of 64.0% as well as a better stability of ∼18 h as compared to L70-Ag-NCs, Ag nanoparticles, and bulk Ag. More importantly, CO generation initiates at an ultralow overpotential of 146 mV, accompanied with a remarkably high onset CO FE of 59.6%, further demonstrating the excellence of L25-Ag-NCs for highly active and selective CO 2 RR. Density functional theory calculations, the percentages of various catalytically active sites, and how the architecture of NCs affecting the active sites as well as the partial density of states were analyzed; the results reveal that the essential origins credited for the enhanced catalytic activity and near-unity CO selectivity over L25-Ag-NCs at lowered η originate from the particular nanostructure, where energetically favorable active sites toward CO 2 RR are maximally introduced through accurately synthesizing the specific nanostructure enclosed by a certain facet.