Realization of Oxygen Reduction and Evolution Electrocatalysis by In Situ Stabilization of Co Nanoparticles in a Redox-Active Donor-Acceptor Porous Organic Polymer

Bifunctional electrocatalysts that can catalyze both oxygen reduction and evolution reactions have high significance in the development of energy storage materials such as fuel cells and metal-air batteries. Here, we have designed and synthesized a redox active porous organic polymer (TAPA-PG) by the Schiff base condensation reaction between 4,4 ',4 ''-triaminotriphenylamine (TAPA, donor) and 1,3,5-triformylphloroglucinol (PG, acceptor). The TAPA-PG possesses permanent microporosity and shows spherical nano-morphologies with diameter of 400-500 nm. TAPA-PG shows electrocatalytic activity towards oxygen reduction reaction (ORR) with an overpotential of 190 mV. Interestingly, TAPA-PG is found to be efficient for in situ reduction of the Co(II) to Co(0) under ambient conditions, and results in a cobalt nanoparticles-stabilized polymer matrix (Co@TAPA-PG). Co@TAPA-PG displays bifunctional electrocatalytic activity for ORR as well as oxygen evolution reaction (OER). Co@TAPA-PG shows improved ORR catalysis as the overpotential dropped down significantly to 120 mV. The OER catalytic performance results in the maximum current density of 15.8 mA/cm(2).The overpotential for OER is found to be 560 mV at the current density of 10 mA/cm(2).