ACS Catal. 7, 2535–2541 (2017)

The non-precious non-porous metal NiFe hydroxide catalyst has been attracting considerable attention for the oxygen evolution reaction (OER) due to its low cost and high catalytic efficiency. Now Li and Zhao have successfully enhanced the wettability while maintaining the structural hierarchy in NiFe hydroxide nanosheets.

Firstly, nanoporous NiFe hydroxide was fabricated onto a carbon fibre paper substrate by electrodeposition. The hydroxide was then partially converted into phosphate by reacting with phosphine (PH3) and H2O vapour released by NaH2PO2·H2O decomposition. The formed NiFe and NiFe phosphate (Pi) worked in synergy for the OER, exhibiting a current density of 10 mA cm−2 at an overpotential of 290 mV, a high current density of 300 mA cm−2 at a low overpotential of 340 mV and a much smaller Tafel slope compared to individual NiFe and Ni:Pi. The improved OER activity of the synergistic NiFe/NiFe:Pi catalyst has three possible explanations. One possibility is the easier water adsorption arising from the greatly improved surface wettability; another is the increased electrochemical surface area induced by phosphorylation; finally it could be due to the enhanced mass transport and charge transfer in the well-maintained 3D hierarchical porous structure. Moreover, this electrocatalyst has been demonstrated to be stable for a long time, without any current density or surface morphology decay even after 1,000 cycles.