Synergy of Ni Nanoclusters and Single Atom Site: Size Effect on the Performance of Electrochemical CO2 Reduction Reaction and Rechargeable Zn−CO2 Batteries

Abstract The design of bifunctional electrocatalysts toward reduction reaction of carbon dioxide (ECO 2 RR) and oxygen evolution reaction (OER) in aqueous rechargeable Zn─CO 2 batteries (ZABs) still poses a significant challenge. Herein, Ni clusters (Ni x ) of 0.5 and 0.8 nm in diameter coupled with single Ni site (Ni−N 4 −C), denoted as Ni−N 4 /Ni 5 and Ni−N 4 /Ni 8 , respectively, are synthesized and the size effect of Ni nanoclusters are studied. Ni−N 4 /Ni 5 exhibits an ≈100% Faradaic efficiency ( FE CO ) toward ECO 2 RR for CO from −0.4 to −0.8 V versus the reversible hydrogen electrode, superior to that of Ni−N 4 −C ( FE CO = 55.0%) and Ni−N 4 /Ni 8 ( FE CO = 80.0%). The OER performance of Ni−N 4 /Ni 5 and Ni−N 4 /Ni 8 are superior or comparable to that of commercial RuO 2 but outperform that of Ni−N 4 −C. Theoretical calculation indicates that * COOH of ECO 2 RR intermediates bond synergistically with Ni x clusters and Ni−N 4 −C single atom site, promoting the activation of CO 2 and reducing the energy barrier of the potential determining step of ECO 2 RR. Such effect is strongly size‐dependent and larger Ni x nanoclusters result in too strong binding of * COOH intermediates, impede the formation of * CO. As a bifunctional cathode electrocatalyst of rechargeable alkaline aqueous ZABs, Ni−N 4 /Ni 5 exhibits a peak power density of 11.7 mW cm −2 and cycling durability over 1200 cycles and 420 h.