ABSTRACT Water‐mediated photothermal CO 2 reduction to CH 4 is promising for renewable energy storage and carbon neutrality, but its selectivity and efficiency are limited by sluggish water dissociation that serves as a critical proton source and the demanding eight‐electron transfer barrier of CH 4 formation. These issues lead to insufficient protons for *CO hydrogenation. Herein, we engineer subnanoscale CeO 2 ‐Cu 2 O heterostructured subnanowires with densely enriched CeO 2 ‐Cu 2 O interfaces to overcome this proton bottleneck. Experimental and theoretical simulation results demonstrate that these interfaces accelerate H 2 O dissociation and create a “proton‐rich microenvironment,” which boosts the proton supply rate to match the kinetic demand of *CO hydrogenation. This directs the protonation of *CO to *CHO instead of CO desorption; these intermediates then convert to *CH 2 O and *CH 3 O, achieving over 99% CH 4 selectivity and a record yield of 2818 μmol g −1 h −1 . This yield is 15‐fold higher than that of bulk and nanoparticle counterparts, underscoring the key role of subnanoscale interface enrichment in optimizing multielectron reactions.
Nie et al. (Sun,) studied this question.