Synergy between Cobalt–Chromium-Layered Double Hydroxide Nanosheets and Oxidized Carbon Nanotubes for Electrocatalytic Oxygen Evolution

Abstract

Enormous potential loss and sluggish kinetics of the oxygen evolution reaction (OER) limit the practical implementation of water electrolyser systems. We attempt to address these technical challenges through the synthesis of cobalt–chromium-layered double hydroxide nanosheets (CoCr LDH) on oxidized-carbon nanotube (O-CNT) backbones as efficient OER electrocatalysts. Microscopic and elemental distribution analysis suggests that interconnected sheets of CoCr LDH masks over O-CNTs. We tested various compositions of the CoCr LDH_O-CNT hybrid (by varying the molar ratios of Co and Cr) along with the weight adjustment between CoCr LDH and O-CNTs to obtain an optimal OER activity. Due to the synergistic effect, the CoCr-LDH(3:1)_O-CNT (2:1) exhibits the lowest overpotential of 290 mV at 10 mA cm–2 with a corresponding smaller Tafel slope of 42 mV dec–1, which outperforms the other tested materials. The catalytically active site of Co2+ is boosted by Cr3+ as a charge transfer site owing to the spin–spin coupling between 3d7 of Co and 3d3 of Cr3+, which is evidenced by electron paramagnetic resonance results. Furthermore, the mildly oxidized carbon nanotubes offer the conducting channels to CoCr-LDH for faster charge transfer during OER.