Proton exchange membrane (PEM) water electrolysers promise efficient production of high-purity hydrogen. Moreover, due to their rapid dynamic responsiveness, they are also ideal for coupling to renewable power sources. However, the acidic nature of the reaction environment in a PEM electrolyser causes corrosion in many materials and has limited the choice of catalyst used at the anode (where O2 is generated) largely to those based on iridium, a rare and expensive metal. For example, while cobalt-based oxides have been suggested to have activity approaching iridium, their stability is typically poor due to cobalt ion dissolution. Now, F. Pelayo García de Arquer and colleagues in Spain, France and the UK report an iridium-free, delaminated cobalt tungstate catalyst that can operate in an 80 °C PEM electrolyser for 608 h at a current density of 1 A cm–2.
The researchers synthesize CoWO4 hydrothermally, before dispersing it in 0.1 M KOH; this treatment leads to a delaminated, flake-like structure with a large number of vacancies due to leaching of WO42– anions. The team find that the delaminated material contains a high density of trapped water and hydroxide groups, which — in contrast to Co3O4 — makes the dissolution of cobalt ions thermodynamically unfavourable. This durability is reflected in the strong stability observed in both standard two-compartment electrochemical cell tests and PEM electrolyser runs. The activity of the catalyst is also notable, with the researchers recording a current density of 1.8 A cm–2 at 2 V in the PEM electrolyser.
This is a preview of subscription content, access via your institution
