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 (Rct) was investigated. The electrochemical dynamic behavior of bivalent CoII 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 CoII is irreversibly oxidized to CoIIIOOH at interface in the first anodic polarization process prior to the occurrence of OER. The surface reconstruction with the formation of CoIIIOOH species reduces the Rct and favors the oxidation conversion of NiII hydroxide into NiIII(oxy)hydroxide at a relatively lower applied potential. The co-existence of these high-valence-state metals (CoIII and NiIII) 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−2 Geo and a Tafel slop of 66 mV dec−1, as well as has a higher iECSA 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.