Ultrathin Nanosheet-Assembled Co-Fe Hydroxide Nanotubes: Sacrificial Template Synthesis, Topotactic Transformation, and Their Application as Electrocatalysts for Efficient Oxygen Evolution Reaction

Hydrogen as a reliable, sustainable, and efficient energy carrier can effectively alleviate global environmental issues and energy crisis. However, the electrochemical splitting of water for large-scale hydrogen generation is still impeded by the sluggish kinetics of the oxygen evolution reaction (OER) at the anode. Considering the synergistic effect of Co and Fe on the improvement of OER catalytic activity, we prepared Co-Fe hydroxide nanotubes through a facile sacrificial template route. The resultant Co_0.8Fe_0.2 hydroxide nanotubes exhibited remarkable electrocatalytic performance for OER in 1.0 M KOH, with a small overpotential of about 246 mV at 10 mA cm^-2 and a Tafel slope of 53 mV dec^-1. The Co_0.8Fe_0.2P nanotubes were further prepared by a phosphidation treatment, exhibiting excellent OER catalytic performance with an overpotential as low as 240 mV at 10 mA cm^-2. Besides, the Co_0.8Fe_0.2P nanotubes supported on a Ni foam (Co_0.8Fe_0.2P/NF) used as both positive and negative poles in a two-electrode system achieved a cell voltage of about 1.67 V at 10 mA cm^-2 and exhibited outstanding stability. A water splitting system was constructed by Co_0.8Fe_0.2P/NF electrodes connected with a crystalline silicon solar cell, demonstrating the application as an electrocatalyst.