Mn3+ Active Surface Site Enriched Manganese Phosphate Nano-polyhedrons for Enhanced Bifunctional Oxygen Electrocatalyst

Manganese-based electrocatalyst has a great attention for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) applications, since the discovery of active centre in nature photosynthesis system. The Mn oxidation state optimization and structural defect engineering are essential to get a highly active Mn-based catalytic materials. MnP showed a good water oxidation activity with a lower overpotential of 286 mV to reach the current density of 10 mA/cm(2) and a Tafel slope of 76 mV/dec. Also, the electron transfer number calculated from both the rotating disk electrode and rotating ring-disk electrode techniques is a quasi-4 electron transfer process with an onset and halfwave potential of 0.998 V and 0.936 V vs RHE respectively. MnP achieved a higher limiting kinetic current of 5.7 mA/cm(2) and a very low H2O2 yield of 1.6 %. Chronoamperometry and cyclic voltammetry studies confirmed the long-term stability and durability of the prepared catalyst. The variance metrics Delta E [Ej(10)-Ej(-3)] is used to estimate the overall activity from the potential difference between OER overpotential at 10 mA/cm(2) and ORR kinetic current at 3 mA/cm(2). MnP shows very low Delta E (0.58 V) which demonstrate an efficient bifunctional activity in ORR and OER reactions. This work might shed new light on the development of MnP based bifunctional oxygen electrocatalyst.