Bifunctional oxovanadate doped cobalt carbonate for high-efficient overall water splitting in alkaline-anion-exchange-membrane water-electrolyzer

Abstract

Large scale, cost-efficient, durable, and non-noble metal catalysts for overall water splitting in alkaline-anionexchange-membrane-water-electrolyzer (AAEMWE) are highly demanded for the clean hydrogen economy. Meanwhile, V- and Co-based bimetallic oxide materials were rarely reported for overall water splitting in AAEMWE. Herein, we demonstrate that the self-supported oxovanadate-doped cobalt carbonate (VCoCOx@NF) on nickel foam (NF) is a high-performance overall water-splitting catalyst in AAEMWE. The as-prepared VCoCOx@NF catalyst demonstrates high activity for both hydrogen and oxygen evolution reactions (HER and OER) in alkaline media, with a current density (j) of 10 mA cm-2 at overpotentials of 63 mV and 240 mV, respectively. Assembled as a conventional electrolyzer for overall water splitting, VCoCOx@NF as both anode and cathode in 1 M KOH operates at low cell voltages of 1.54 and 1.74 V at 10 and 100 mA cm-2, respectively, superior to the Ir/ C-Pt/C@NF electrolyzer (1.59 and 1.86 V, respectively). First principle calculations show that the remarkable HER and OER at the Co site are due to the doping of V species, which reduces the overpotential by shifting the delectron states of Co towards the Fermi-level. Besides, an AAEMWE cell fabricated with the VCoCOx@NF catalyst delivers j = 200 mA cm-2 at 2.01 V in deionized water, lower than the expensive commercial IrOx-Pt/C@Au/Ti electrolyzer (2.06 V). This finding provides the stage for large-scale hydrogen production by utilizing the V- and Co-based bimetallic oxide materials.