Bifunctional porous cobalt phosphide foam for high-current-density alkaline water electrolysis with 4000-hour long stability

Alkaline water electrolysis is a cost-effective approach to hydrogen production, but it suffers from low operational current densities (typically ⤠500 mA cm-2) and thereby a low hydrogen production rate. Herein, we report the fabrication of self-supported porous cobalt phosphide (Co-P) foam by electrochemical anodization of commercially available cobalt foam, followed by thermal oxidation and subsequent phosphorization. The as-obtained porous Co-P foam, compared to other control samples prepared under different conditions, shows outstanding electrocatalytic performance in alkaline electrolyte for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), requiring an overpotential of 290 mV for HER and 380 mV for OER, respectively, at a high current density of 1000 mA cm-2. Moreover, the electrolyzer consisting of two symmetric porous Co-P foam electrodes only requires a cell voltage of 1.98 V to operate at 1000 mA cm-2 for overall water electrolysis, with extraordinary stability of 4000 h, showing great potential for use in industrial alkaline water electrolysis. L. Liu acknowledges the financial support of Fundação para a Ciência e a Tecnologia (FCT, Portugal) Exploratory Grant (IF/01595/2014/CP1247/CT0001) and I.C.N. thanks to project BioTecNorte (operation NORTE-01-0145-FEDER-000004) and Centre of Chemistry, University of Minho (UID/QUI/00686/2013 and UID/QUI/0686/2016). Z. P. Yu acknowledges the financial support of China Scholarship Council (Grant No. 201806150015).