Study of the Active Sites in Porous Nickel Oxide Nanosheets by Manganese Modulation for Enhanced Oxygen Evolution Catalysis

Identifying active sites of oxygen evolution reaction catalysts is essential for studying water oxidation mechanisms. Herein, the active site of nickel oxide nanosheets by manganese modulation is investigated in an electrocatalytic oxygen evolution system. The electronic structure could be realized by Mn modulation. The intrinsic catalytic activity of Ni3+ (t2g6eg1) and Jahn–Teller active Mn3+ (t2g3eg1) species act synergistically to promote the elctrocatalytic oxygen evolution reaction. X-ray absorption near-edge structure analysis indicates that the Ni3+ and Mn3+ in Ni0.75Mn0.25 nanosheets should result from nickel vacancies and oxygen vacancies, respectively. The resulting Ni0.75Mn0.25 nanosheets show much higher oxygen evolution activity than those of NiO and Mn2O3. Density functional theory calculations indicate that the Ni and Mn act synergistically to promote formation of the O–O bond. Our work provides a comprehensive understanding of the active site of porous nickel oxide nanosheets by manganese modulation and rational design of electrocatalysts with precisely engineered structures and electrical properties.