Electrodeposition and Characterization of CoP Compounds Produced from the Hydrophilic Room-Temperature Ionic Liquid 1-Butyl-1-Methylpyrrolidinium Dicyanamide

The voltammetric behaviors of Co(II), H 2 PO 2 − , and their mixtures in four molar ratios were studied in the hydrophilic room-temperature ionic liquid (RTIL) 1-butyl-1-methylpyrrolidinium dicyanamide ([BMP][DCA]). Co(II) was introduced into the RTIL via Co-metal anodization or the addition of CoSO 4 , respectively, while NaH 2 PO 2 was used as the H 2 PO 2 − source. A single redox couple of Co(II)/Co was observed in the RTIL containing Co(II). Although elemental phosphorus (P) cannot be directly electrodeposited from NaH 2 PO 2 , CoP was successfully obtained via potentiostatic electrodeposition from [BMP][DCA] containing both CoSO 4 and NaH 2 PO 2 . The obtained Co and CoP electrodeposits were both characterized to study the effects of electrodeposition potential on their surface morphology, elemental composition, crystallinity, and electrocatalytic activity. The as-deposited Co and CoP both showed amorphous features in X-ray diffraction analysis, and crystalline diffraction signals were observed after they were annealed at 623 K for 2 hours. The crystalline structures of the as-deposited CoP, however, were observed using high-resolution TEM, indicating a nanometer-domain crystal size. The oxygen evolution reaction (OER) was studied at the Pt electrode, Co-, and CoP-coated copper electrodes, of which the Co ∼70 P 30∼ electrode showed the best electrocatalytic activity toward OER.