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

Abstract

AbstractThe design of bifunctional electrocatalysts toward reduction reaction of carbon dioxide (ECO2RR) and oxygen evolution reaction (OER) in aqueous rechargeable Zn─CO2 batteries (ZABs) still poses a significant challenge. Herein, Ni clusters (Nix) of 0.5 and 0.8 nm in diameter coupled with single Ni site (Ni−N4−C), denoted as Ni−N4/Ni5 and Ni−N4/Ni8, respectively, are synthesized and the size effect of Ni nanoclusters are studied. Ni−N4/Ni5 exhibits an ≈100% Faradaic efficiency (FECO) toward ECO2RR for CO from −0.4 to −0.8 V versus the reversible hydrogen electrode, superior to that of Ni−N4−C (FECO = 55.0%) and Ni−N4/Ni8 (FECO = 80.0%). The OER performance of Ni−N4/Ni5 and Ni−N4/Ni8 are superior or comparable to that of commercial RuO2 but outperform that of Ni−N4−C. Theoretical calculation indicates that *COOH of ECO2RR intermediates bond synergistically with Nix clusters and Ni−N4−C single atom site, promoting the activation of CO2 and reducing the energy barrier of the potential determining step of ECO2RR. Such effect is strongly size‐dependent and larger Nix 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−N4/Ni5 exhibits a peak power density of 11.7 mW cm−2 and cycling durability over 1200 cycles and 420 h.