Facile synthesis of defect-rich ultrathin NiCo-LDHs, NiMn-LDHs and NiCoMn-LDHs nanosheets on Ni foam for enhanced oxygen evolution reaction performance

Layered double hydroxides (LDHs) containing transition metals with unsaturated d-bands are ideal candidates for oxygen evolution reaction (OER). However, the bulk layers and congested interlayers block the active sites and avoid the electrolyte access to the internal space. In this work, we report a simple coprecipitation coupled with the hydrothermal method for the direct growth of bimetallic NiCo-LDHs (5.01 nm), NiMn-LDHs (3.45 nm) and trimetallic NiCo-Mn-LDHs nanosheets (1.26 nm) on Ni foam and these fabricated electrodes exhibit the superior performance for OER. Notably, the NiCoMn-LDHs nanosheets exhibit the lowest overpotential of 290 mV at 20 mA cm(-2) and the smallest Tafel slope of 87 mV dec(-1), reducing by 20-40 mV and 31-39 mV dec(-1) in comparison with those of bimetallic NiCo-LDHs (310 mV, 118 mV dec(-1)) and NiMn-LDHs (330 mV, 126 mV dec(-1)). This excellent performance is attributed to the 2D structure of the nanosheets and an abundance of exposed active sites, especially oxygen vacancies. Additionally, NiCoMn-LDHs nanosheets exhibit the smallest charge transfer resistance (R-ct) of 6.3 Omega and the largest electrochemical double layer capacitance (C-dl) of 5.52 mF cm(-2) than those of the bimetallic NiCo-LDHs (11.0 Omega, 4.85 mF cm(-2)) and NiMn-LDHs (30.6 Omega, 3.00 mF cm(-2)). Furthermore, NiCoMn-LDHs nanosheets maintain good durability over 10 h and cyclic stability without distinct change. This work offers a facile strategy to design various types of bimetallic and trimetallic LDHs boosting for OER process. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

In this study, bimetallic and trimetallic LDHs nanosheets were successfully prepared using coprecipitation coupled with the hydrothermal method, exhibiting superior performance for OER. Among them, NiCoMn-LDHs nanosheets showed the lowest overpotential and smallest Tafel slope, attributed to the exposed active sites and oxygen vacancies for efficient oxygen evolution.