NiCo-layered double hydroxides embedded with trace platinum species for boosting alkaline hydrogen evolution reaction

Abstract

Reducing the amount of platinum (Pt) and improving the efficiency of the hydrogen evolution reaction (HER) in alkaline media is a key issue for the industrial production of hydrogen. Unlike HER under acidic conditions, the hydrogen adsorbed-atom (Had) has to be discharged from the water molecule rather than from the hydronium cation (H3O+). Pt catalysts have outstanding H adsorption and desorption free energy but are not conducive to catalyze the dissociation of water, which is the main reason for their hysteresis in alkaline HER. The combination of Pt and a cocatalyst effectively cleave the O–H bonds is an effective strategy to improve the reaction kinetics in the alkaline HER. Currently, in an alkaline electrolyte, non-noble metal hydroxide catalysts are very active for oxygen evolution reaction (OER), especially the Ni–Co hydroxide (NiCoOxHy), which effectively promotes OER owing to its excellent water dissociation ability. In this work, in a three-electrode system, a Pt wire counter electrode was used as the Pt source. Cyclic voltammetry (CV) electrochemical deposition was used to load a trace amount of Pt species onto the NiCo-layered double hydroxides (NiCo-LDHs) prepared using hydrothermal reaction on a nickel foam substrate. NiCo-LDHs can promote the dissociation of water in alkaline media, and Pt sites are beneficial for the binding and desorption of H on the electrode surface. The combination of Pt and NiCo-LDHs effectively paves a new way to enhance the slow kinetics of the hydrogen evolution reaction of Pt in an alkaline medium. The hybrid catalyst Pt‒NiCo-LDHs shows considerably improved HER performance, with a small overpotential of 56 mV to drive a typical current density of 10 mA·cm−2 and a low Tafel slope of 43 mV·decade−1 in alkaline media at an ultralow Pt loading of 30.4 g·cm−2. The mass activity of Pt‒NiCo-LDHs is 5.6 times higher than that of a commercial Pt/C catalyst with a 100 mV overpotential. Moreover, the Pt‒NiCo-LDHs catalyst exhibits outstanding stability after a 100 h test.

Keywords

• nico-layered double hydroxides
• hydrogen evolution reaction
• electrocatalytic activity
• hydrothermal method
• electrochemical deposition