Electrocatalytic semihydrogenation of acetylene provides a clean pathway to produce ethylene (C 2 H 4 ), one of the most widely used petrochemical feedstocks, but its performance is still well below that of the thermocatalytic route, leaving its practical feasibility questionable. Here our techno-economic analysis shows that this process becomes pro table if the Faraday e ciency (FE) exceeds 85% at a current density of 0.2 A cm −2 . As a result, we design a Cu nanoparticle catalyst with coordinatively unsaturated sites to steer the reaction towards these targets. Remarkably, our electrocatalyst synthesized on gas diffusion layer-coated carbon paper enables a high C 2 H 4 yield rate of 70.15 mmol mg −1 h −1 and a FE of 97.7% at an industrially relevant current density of 0.5 A cm −2 . Combined characterizations and calculations reveal that such performance can be attributed to a favorable combination of a higher energy barrier for coupling of active hydrogen atoms (H*) and weak absorption of *C 2 H 4 . The former serves to suppress the competitive hydrogen evolution reaction, whereas the latter avoids overhydrogenation and C-C coupling. Further life cycle assessment evidences the economic feasibility and sustainability of the process. Our work suggests a way towards rational design and manipulation of nanocatalysts that could nd wider and greener catalytic applications.

Electrocatalytic semihydrogenation of acetylene provides a clean pathway to produce ethylene (C2H4), one of the most widely used petrochemical feedstocks, but its performance is still well below that of the thermocatalytic route, leaving its practical feasibility questionable. Here our techno-economic analysis shows that this process becomes profitable if the Faraday efficiency (FE) exceeds 85% at a current density of 0.2 A cm−2. As a result, we design a Cu nanoparticle catalyst with coordinatively unsaturated sites to steer the reaction towards these targets. Remarkably, our electrocatalyst synthesized on gas diffusion layer-coated carbon paper enables a high C2H4 yield rate of 70.15 mmol mg−1 h−1 and a FE of 97.7% at an industrially relevant current density of 0.5 A cm−2. Combined characterizations and calculations reveal that such performance can be attributed to a favorable combination of a higher energy barrier for coupling of active hydrogen atoms (H*) and weak absorption of *C2H4. The former serves to suppress the competitive hydrogen evolution reaction, whereas the latter avoids overhydrogenation and C-C coupling. Further life cycle assessment evidences the economic feasibility and sustainability of the process. Our work suggests a way towards rational design and manipulation of nanocatalysts that could find wider and greener catalytic applications.