Porous Mn-doped cobalt phosphide nanosheets as highly active electrocatalysts for oxygen evolution reaction

Abstract

Transition metal phosphides (TMP) show great potential to alternative noble metal based electrocatalysts for oxygen evolution reaction (OER) electrolysis but the still unsatisfactory catalytic activity hinders its practical application. Therefore, it is of much significance to rationally design TMP electrocatalysts for achieving high-efficiency OER. Here, we design Mn-doped cobalt phosphide (Mn-CoP) porous nanosheets for highly active OER through the in-situ metal acetate hydroxide transformation and subsequent phosphidation treatment. Benefiting from synergistic effects of the porous structure, high density of active sites and improved charge-transfer capability, the optimized Mn-CoP serving as a pre-catalyst shows an impressive alkaline OER performance with a low overpotential of 288 mV at the current density of 10 mA cm−2 and high stability. Post-electrolysis characterizations show the conversion from Mn-CoP to vertical Mn-CoOOH hexagonal nanosheets during OER, in which the transformed Mn-CoOOH not only provide extra active sites, but serve as the highly active species. Density functional theory (DFT) calculations reveal that Mn doping can increase the gap states near the Fermi level of active O sites, endowing facilitated deprotonation of OH* to O* and reducing the energy barrier of rate-determining step. This protocol provides a novel insight for the construction of highly efficient TMP water oxidation electrocatalysts.