Flower-like CoP microballs assembled with (002) facet nanowires via precursor route: Efficient electrocatalysts for hydrogen and oxygen evolution

Abstract It is important to prepare an environmental-friendly and earth-abundant electrocatalyst with excellent performance and superior stability for efficient hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, a facile precursor route is developed to synthesize CoP nanostructure with different morphologies just by controlling the hydrothermal reaction temperature and time. The precursor Co(CO 3 ) 0.5 OH·0.11H 2 O (CHCH) nanowire (NW) and uniform flower-like microball (MB) with exposed (001) facet were firstly successfully prepared at hydrothermal reaction temperature of 115 °C for 3 h and 10 h, respectively. And then a phosphorization treatment of CHCH was performed to get CoP NWs and flower-like CoP MBs assembled with ordered NWs that exposed (002) facets. The CoP MBs exhibit a lower over-potential of 105.3 mV at the current density of 10 mA cm −2 , and a smaller Tafel slope of 53.5 mV·dec −1 in 0.5 M H 2 SO 4 solution for HER. Furthermore, this hierarchical structure could possess its good activity for 40,000 s. The catalyst also shows an excellent activity with the overpotential of 97.3 mV at 10 mA cm −2 , and a Tafel slope of 84.3 mV·dec −1 in 1 M KOH solution for HER. The density functional theory (DFT) calculations further reveal that hydrogen adsorbed on all P sites of CoP could result in smaller adsorption energy (0.085 eV), which is comparable to Pt. So, all P sites are the main active sites for HER. Also, these flower-like CoP MBs could display a good electrocatalytic activity for OER. Compared to disordered CoP NWs, the flower-like CoP MBs exhibit a better HER and OER performance because this hierarchical structure possessed two merits, that is, the fast vectorial electron transfer along the ordered NWs and improved inherent activity of each active site due to the exposed (002) facet. This low-cost and high-activity hierarchical structure is an efficient catalyst for HER and OER.