Self-Tandem Electrocatalytic NO Reduction to NH 3 on a W Single-Atom Catalyst.

We design single-atom W confined in MoO 3- x amorphous nanosheets (W 1 /MoO 3- x ) comprising W 1 -O 5 motifs as a highly active and durable NORR catalyst. Theoretical and operando spectroscopic investigations reveal the dual functions of W 1 -O 5 motifs to (1) facilitate the activation and protonation of NO molecules and (2) promote H 2 O dissociation while suppressing *H dimerization to increase the proton supply, eventually resulting in a self-tandem NORR mechanism of W 1 /MoO 3- x to greatly accelerate the protonation energetics of the NO-to-NH 3 pathway. As a result, W 1 /MoO 3- x exhibits the highest NH 3 -Faradaic efficiency of 91.2% and NH 3 yield rate of 308.6 μmol h -1 cm -2 , surpassing that of most previously reported NORR catalysts.