Charge induced crystal distortion and morphology remodeling: Formation of Mn-CoP nanowire @ Mn-CoOOH nanosheet electrocatalyst with rich edge dislocation defects

Abstract Cobalt phosphide (CoP), as a potential electrocatalyst candidate for hydrogen evolution reaction (HER) as well as oxygen evolution reaction (OER), attracts rising interest. However, its intrinsic catalytic activity is still not comparable with those noble-metal-based ones while its surface species is easily oxidized to amorphous phosphate in air. Herein, abundant edge dislocations were successfully generated on the Mn doped CoP material with an electrochemical reduction process, leading to the formation of P vacancies, and lattice distortion, resulting in the modification of the electronic structure and the improvement of the whole catalysis performance. Based on the density functional theory (DFT) calculations, it is found that the P vacancies on the edge dislocation could change the Gibbs free energy, enhancing the intrinsic catalytic activity of Mn-CoP. Furthermore, the surface of Mn-CoP was in-situ converted to Mn-CoOOH with a nanosheet structure by an electrochemical oxidization, resulting in a Mn-CoP nanowire @ Mn-CoOOH nanosheet core@shell structure. The formed Mn-CoOOH nanosheet shell not only effectively prevented the continuous oxidation of Mn-CoP but also provided additional catalytic active sites for OER. Besides, the Mn-CoOOH was reduced to Mn-Co(OH)2 as the real active species during HER, which effectively promoted the decompsition of water to proton. As a result, such a defect-activated Mn-CoP nanowire @ Mn-CoOOH nanosheet electrocatalyst needed low overpotentials of 106 and 251 mV to support a current density of 10 mA cm-2 for HER and OER with high stability, respectively.