High efficiency overall water splitting enabled by a hierarchical Ni–C structure derived from 2D MOF sheets without heteroatom doping.

Three-dimensional bimetallic nanoframes with high spatial diffusivity and surface heterogeneity possess remarkable catalytic activities owing to their highly exposed active surfaces and tunable electronic structure. Here we report a general one-pot strategy to prepare ultrathin octahedral Au 3 Ag nanoframes, with the formation mechanism explicitly elucidated through well-monitored temporal nanostructure evolution. Rich crystalline defects lead to lowered atomic coordination and varied electronic states of the metal atoms as evidenced by extensive structural characterizations. When used for electrocatalytic methanol oxidation, the Au 3 Ag nanoframes demonstrate superior performance with a high specific activity of 3.38 mA cm −2 , 3.9 times that of the commercial Pt/C. More intriguingly, the kinetics of methanol oxidation on the Au 3 Ag nanoframes is counter-intuitively promoted by carbon monoxide. The enhancement is ascribed to the altered reaction pathway and enhanced OH − co-adsorption on the defect-rich surfaces, which can be well understood from the d-band model and comprehensive density functional theory simulations.

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Electrocatalytic conversion of carbon dioxide into high‐value multicarbon (C2+) chemical feedstocks offers a promising avenue to liberate the chemical industry from fossil‐resource dependence and eventually close the anthropogenic carbon cycle but is severely impeded by the lack of high‐performance catalysts. To break the linear scaling relationship of intermediate binding and minimize the kinetic barrier of CO2 reduction reactions, ternary Cu–Au/Ag nanoframes were fabricated to decouple the functions of CO generation and C−C coupling, whereby the former is promoted by the alloyed Ag/Au substrate and the latter is facilitated by the highly strained and positively charged Cu domains. Thus, C2H4 production in an H‐cell and a flow cell occurred with high Faradic efficiencies of 69±5 and 77±2 %, respectively, as well as good electrocatalytic stability and material durability. In situ IR and DFT calculations unveiled two competing pathways for C2H4 generation, of which direct CO dimerization is energetically favored.

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The electroreduction of carbon dioxide (CO2RR) to CH4 stands as one of the promising paths for resourceful CO2 utilization in meeting the imminent “carbon‐neutral” goal of the near future. Yet, limited success has been witnessed in the development of high‐efficiency catalysts imparting satisfactory methane selectivity at a commercially viable current density. Herein, a unique category of CO2RR catalysts is fabricated with the yolk–shell nanocell structure, comprising an Ag core and a Cu2O shell that resembles the tandem nanoreactor. By fixing the Ag core and tuning the Cu2O envelope size, the CO flux arriving at the oxide‐derived Cu shell can be regulated, which further modulates the *CO coverage and *H adsorption at the Cu surface, consequently steering the CO2RR pathway. Density functional theory simulations show that lower CO coverage favors methane formation via stabilizing the intermediate *CHO. As a result, the best catalyst in the flow cell shows a high CH4 Faraday efficiency of 74 ± 2% and partial current density of 178 ± 5 mA cm−2 at −1.2 VRHE, ranking above the state‐of‐the‐art catalysts reported today for methane production. These findings mark the significance of precision synthesis in tailoring the catalyst geometry for achieving desired CO2RR performance.

The defect engineering of noble metal nanostructures is of vital importance because it can provide an additional yet advanced tier to further boost catalysis, especially for one-dimensional (1D) noble metal nanostructures with a high surface to bulk ratio and more importantly the ability to engineer the defect along the longitudinal direction of the 1D nanostructures. Herein, for the first time, we report that the defect in 1D noble metal nanostructures is a largely unrevealed yet essential factor in achieving highly active and stable electrocatalysts toward fuel cell reactions. The detailed electrocatalytic results show that the Pd–Sn nanowires (NWs) exhibit interesting defect-dependent performance, in which the defect-rich Pd4Sn wavy NWs display the highest activity and durability for both the methanol oxidation reaction (MOR) and the oxygen reduction reaction (ORR). Density functional theory (DFT) calculations reveal that a large number of surface vacancies/agglomerated voids are the driving forces for forming surface grain boundaries (GBs) within Pd4Sn WNWs. These electronic active GB regions are the key factors in preserving the number of Pd0 sites, which are critical for minimizing the intrinsic site-to-site electron-transfer barriers. Through this defect engineering, the Pd4Sn WNWs ultimately yield highly efficient alkaline ORR and MOR. The present work highlights the importance of defect engineering in boosting the performance of electrocatalysts for potentially practical fuel cells and energy applications.

Electrochemical CO2 reduction (CO2RR) in a product-orientated and energy-efficient manner relies on rational catalyst design guided by mechanistic understandings. In this study, the effect of conducting support on the CO2RR behaviors of semi-conductive metal-organic framework (MOF) — Cu3(HITP)2 are carefully investigated. Compared to the stand-alone MOF, adding Ketjen Black greatly promotes C2H4 production with a stabilized Faradaic efficiency between 60-70% in a wide potential range and prolonged period. Multicrystalline Cu nano-crystallites in the reconstructed MOF are induced and stabilized by the conducting support via current shock and charge delocalization, which is analogous to the mechanism of dendrite prevention through conductive scaffolds in metal ion batteries. Density functional theory calculations elucidate that the contained multi-facets and rich grain boundaries promote C–C coupling while suppressing HER. This study underlines the key role of substrate-catalyst interaction, and the regulation of Cu crystalline states via conditioning the charge transport, in steering the CO2RR pathway.