Flexible direct synthesis of phosphorus-rich CoP3 on carbon black and its examination in hydrogen evolution electrocatalysis

In contrast to metal-rich cobalt phosphides, phosphorus-rich CoP3 is less studied as a hydrogen evolution reaction (HER) electrocatalyst, though it has distinct polyphosphide structural features and electronic properties that can be useful in facilitating proton reduction. While bulk crystalline solids are ideal surfaces for electrocatalytic studies, methods to disperse active catalysts on inexpensive high surface area supports can lead to improved HER activity with less catalyst. This paper describes a straightforward two-step procedure to produce a series of crystalline CoP3 particles supported on conducting carbon black powder. Anhydrous CoCl2 was deposited onto carbon black in various amounts from a methanol solution. The dried CoCl2/C products were directly reacted with elemental phosphorus in an ampoule at 500 degrees C. These reactions produce crystalline CoP3/C with nominally 5-25 mol% of CoP3 on carbon black. These CoP3/C composites possess a similar to 3 to 10 times higher surface area (similar to 11-35 m(2) g(-1)) versus similarly synthesized bulk CoP3. The CoP3 crystallites grow in aggregated form with carbon black nanoparticles. The HER electrocatalytic behavior of these composites in 0.5 M H2SO4 was evaluated and all CoP3/C composites were HER active and require only applied potentials near -95 mV to achieve 10 mA cm(-2) current densities. The lower content CoP3 catalyst particles dispersed on carbon black show similar HER activity to bulk CoP3. These CoP3/C composites are stable in acid and show a high degree of electrocatalytic stability in extended time HER electrocatalytic experiments.