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), H2PO2-, 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 CoSO4, respectively, while NaH2PO2 was used as the H2PO2- 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 NaH2PO2, CoP was successfully obtained via potentiostatic electrodeposition from [BMP][DCA] containing both CoSO4 and NaH2PO2. 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 similar to 70P30 similar to electrode showed the best electrocatalytic activity toward OER. (C) The Author(s) 2017. Published by ECS. All rights reserved.