Impact of interfacial CoOOH on OER catalytic activities and electrochemical behaviors of bimetallic CoxNi-LDH nanosheet catalysts

Bimetallic CoNi-LDHs as catalyst candidates for OER have attracted increasing interests due to their high catalytic activities, low cost and earth abundance. In this work, a series of CoxNi-LDH nanosheets were synthesized by a chemical co-precipitation method. The impact of Co roles on OER catalytic activities, oxidation conversion of nickel metal ions and resistance of charge-transfer reactions (R-ct) was investigated. The electrochemical dynamic behavior of bivalent Co-II was characterized by CV and EIS in combination with XPS. The surface morphologies and microstructure were studied by SEM and TEM, respectively. The results show that Co-II is irreversibly oxidized to Co-III OOH at interface in the first anodic polarization process prior to the occurrence of OER. The surface reconstruction with the formation of Co-III OOH species reduces the R-ct and favors the oxidation conversion of Ni-II hydroxide into Ni-III (oxy)hydroxide at a relatively lower applied potential. The co-existence of these high-valence-state metals (Co-III and Ni-III) on the LDH surface further boosts the catalytic activity and enhances the OER performance. The OER activity of the CoxNi-LDHs increases with increase of the Co: Ni ratio, and reaches the maximum as the Co:Ni ratio raises to about 1.8:1.0. The Co1.8Ni-LDH shows the most active OER catalyst with an overpotential of 290 mV at 10 mA cm(Geo)(-2) and a Tafel slop of 66 mV dec(-1), as well as has a higher i(ECSA) and TOF. The carbon-free pasted Co1.8Ni-LDH electrode on Ni foam also exhibits excellent durability at 100 mA cm(-2) in 1M KOH at room temperature. (c) 2021 Elsevier Ltd. All rights reserved.