Evolution of layered double hydroxides (LDH) as high performance water oxidation electrocatalysts: A review with insights on structure, activity and mechanism

Electrocatalytic water oxidation which is otherwise recently popularized as the oxygen evolution reaction (OER) is the significant half-cell reaction in the field of hydrogen generation by water splitting. Being a multistep and a relatively more complex half-cell reaction than its counter hydrogen evolution reaction (HER), OER always requires higher overpotentials than HER. In order to minimize the associated energy loss as overpotentials, these electrochemical half-reactions of water splitting are to be catalyzed with appropriate materials. The recent evolution of transition metals based layered double hydroxides (LDH) as OER catalysts in electrochemical water splitting have lifted the field of H2 generation with the uttermost purity to a greater height. In addition, these materials possess a lot of advantages like being non-precious, gaining excellent catalytic activity and stability in high alkaline solution along with the ease of preparation methods. With all those LDH materials used in electrochemical and photoelectrochemical water splitting, the presence of any of the three iron group metals (Ni, Co and Fe) is essentially seen. In this review, a detailed view on the basics of OER electrocatalysis, evaluation perspectives, current trends in OER electrocatalysis, evolution of these LDH materials as OER catalysts, activity trends, relationship among structure, activity and mechanism, trends in the synthesis methodologies, dominance of Ni–Fe LDH materials in OER electrocatalysis and the challenges and opportunities have been elaborated in detail.