Electrochemical water splitting utilizing renewable electricity is a promising technology for the production of clean and sustainable hydrogen. The most active electrocatalyst for the hydrogen evolution reaction (HER) is platinum. However, the high costs and scarcity associated with platinum motivate the search for alternative catalysts.¹ Promising HER activities have been reported for many families of materials including transition metal chalcogenides, carbides and in particular, phosphides.² Specifically, cobalt phosphide (CoP) is an interesting and active non-precious metal HER catalyst in acid media.³

In this work we synthesise active and stable CoP catalysts on carbon supports at the 1 – 5 g batch scale. The CoP catalysts are prepared by wetness impregnation Vulcan carbon followed by a red phosphorous based vapour phase phosphidation. The crystal structure and chemical composition of the CoP catalyst is verified by XPS and XRD. The morphology of the catalyst is shown to consist of <20 nm particles on the surface of Vulcan carbon support by SEM. The synthesised CoP catalysts are first screened by laboratory scale three-electrode electrochemistry and demonstrate good activity for HER requiring an overpotential of 154 mV to reach -10 mA.cm^-2. Beyond three-electrode laboratory scale electrochemistry screening, the most active and durable HER catalysts were used to fabricate 25 cm² single cell stack membrane electrode assemblies (MEA). The performance of the CoP MEAs was assessed by polarization curve as well as steady state measurements at various current densities and were found to be stable for >20 h of testing. This work highlights the remarkable stability and promise of transition metal phosphides in an MEA configuration.

References

(1) Ng, J. W. D.; Hellstern, T. R.; Kibsgaard, J.; Hinckley, A. C.; Benck, J. D.; Jaramillo, T. F. ChemSusChem 2015, 8 (20), 3512.

(2) Seh, Z. W.; Kibsgaard, J.; Dickens, C. F.; Chorkendorff, I.; Nørskov, J. K.; Jaramillo, T. F. Science 2017, 355 (6321), eaad4998.

(3) Hellstern, T. R.; Benck, J. D.; Kibsgaard, J.; Hahn, C.; Jaramillo, T. F. Adv. Energy Mater. 2016, 6 (4), 1501758.