Electronic Band Structure Engineering of Transition Metal Oxide‐N,S‐Doped Carbon Catalysts for Photoassisted Oxygen Reduction and Oxygen Evolution Catalysis

Abstract

AbstractA novel “dual isolation of metal active sites” heterojunction engineering is developed in this work. The double isolation of the active sites is achieved through MN4 (M = Co, Fe) coordinating bonds in sulfonated‐substituted metalloporphyrin (MTPPS) and electrostatic interactions of MTPPS absorbed with poly(3,4‐ethylenedioxythiophene) networks. Subsequent “in situ copyrolysis” over the precursors ensures effective contact between p‐type CoFe2O4 and n‐type Fe2O3 species with n‐type N,S‐doping carbon support, respectively. This leads to p–n CoFe2O4‐N,S‐C and n–n Fe2O3‐N,S‐C heterojunctions. Meanwhile, CoFe2O4‐N,S‐C has a higher EVB energy level (−6.22 eV) than Fe2O3‐N,S‐C (−6.31 eV), achieving lower energy barrier, and thus superior oxygen reduction reaction (ORR) performance with a higher half‐wave potential (0.84 V) of CoFe2O4‐N,S‐C than Fe2O3‐N,S‐C (0.82 V). In addition, CoFe2O4‐N,S‐C also exhibits higher oxygen evolution reaction (OER) performance with 100 mV lower overpotential (0.41 V) than Fe2O3‐N,S‐C. The lower overpotential is a result of larger energy gap between ECB energy level and Fermi level of CoFe2O4‐N,S‐C. This is the first demonstration of a novel p–n heterojunction with a special band structure that plays a key role in highly active ORR and OER bifunctional catalysis. Moreover, CoFe2O4‐N,S‐C displays significant photoelectrochemical enhancement upon light irradiation.