Hierarchical Tandem Catalysis Promotes CO Spillover and Trapping for Efficient CO Reduction to C Products.

The electrochemical CO reduction reaction (CORR) to produce multicarbon (C) hydrocarbons or oxygenate compounds is a promising route to obtain a renewable fuel or valuable chemicals; however, producing C at high current densities is still a challenge. Herein, we design a hierarchically structured tandem catalysis electrode for greatly improved catalytic activity and selectivity for C products. The tandem catalysis electrode is constructed of a sputtered Ag nanoparticle layer on a hydrophobic polytetrafluoroethylene (PTFE) membrane and a layer of nitrogen-doped carbon (NC)-modified Cu nanowire arrays. The Cu nanowire arrays are grown on PTFE by electrochemical oxidation of sputtered CuAl alloy, in which the chemical etching of metal Al induces the formation of a Cu nanowire array structure. Within hierarchical configuration, CO can be efficiently generated on an active Ag layer and then spillover and transfer to NC-modified Cu nanowire array layer, in which Cu/NC interfaces can enhance *CO trapping and adsorption. During the CORR, the optimized tandem catalysis electrode achieves superior Faradaic efficiencies of 53.5% and 87.5% for ethylene (CH) and C products at the current density of 519.0 mA cm, respectively, with a high C/C ratio of 10.42 and long-term stability up to 50 h. Raman and attenuated total reflection-surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) confirm that the Ag-Cu-NC tandem catalysis system significantly enhances the linear adsorption of *CO intermediates and the dissociation of HO, improves the C-C coupling capability, and stabilizes the key intermediate *OCCOH to produce C products.