Electrochemical carbon monoxide reduction is a promising strategy for the production of value-added multicarbon compounds, albeit yielding diverse products with low selectivities and Faradaic efficiencies. Here, copper single atoms anchored to Ti3C2Tx MXene nanosheets are firstly demonstrated as effective and robust catalysts for electrochemical carbon monoxide reduction, achieving an ultrahigh selectivity of 98% for the formation of multicarbon products. Particularly, it exhibits a high Faradaic efficiency of 71% towards ethylene at −0.7 V versus the reversible hydrogen electrode, superior to the previously reported copper-based catalysts. Besides, it shows a stable activity during the 68-h electrolysis. Theoretical simulations reveal that atomically dispersed Cu–O3 sites favor the C–C coupling of carbon monoxide molecules to generate the key *CO-CHO species, and then induce the decreased free energy barrier of the potential-determining step, thus accounting for the high activity and selectivity of copper single atoms for carbon monoxide reduction.

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The electrochemical reduction of N 2 to NH 3 is emerging as ap romising alternative for sustainable and distributed production of NH 3 .H owever,t he development has been impeded by difficulties in N 2 adsorption, protonation of *NN,a nd inhibition of competing hydrogen evolution. To address the issues,w ed esign ac atalyst with diatomic Pd-Cu sites on N-doped carbon by modulation of single-atom Pd sites with Cu. The introduction of Cu not only shifts the partial density of states of Pd toward the Fermi level but also promotes the d-2p*c oupling between Pd and adsorbed N 2 ,l eading to enhanced chemisorption and activated protonation of N 2 ,and suppressed hydrogen evolution. As ar esult, the catalyst achieves ah igh Faradaic efficiency of 24.8 AE 0.8 %a nd ad esirable NH 3 yield rate of 69.2 AE 2.5 mgh À1 mg cat. À1 ,f ar outperforming the individual single-atom Pd catalyst. This work paves ap athway of engineering single-atom-based electrocatalysts for enhanced ammonia electrosynthesis.