Iron Phosphide Nanoparticles As an Efficient Electrocatalyst for the Oxygen Evolution Reaction in Alkaline Solution

Abstract

Splitting water to hydrogen and oxygen through hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is basis to feed the fuel cell. OER is a thermodynamically uphill process as it requires higher potential to form O2 molecule. The best known catalysts to split water with low overpotential are the oxides of Ir and Ru. As these catalysts are precious metals there has been intensive research to substitute them with earth-abundant resources. The new catalyst should fulfill the following: (i) the catalyst to split water has to use minimal energy (measured as applied voltage and referred to as overpotential); (ii) should comprise of earth abundant elements; (iii) should be stable; (iv) should be scalable.1 Transition metal oxides have been recently identified as high-efficiency catalysts for oxygen and/or hydrogen evolution reaction. Apart from the oxides there has been reports of sulfide, selenide and nitride based catalysts.2 Although transition metal phosphides has recently gathered attention as HER catalysts,3 very less metal phosphides have been reported as OER electrocatalyst. In this presentation, ultra-small iron phosphide nanoparticles as well nanoparticle composite with reduced graphene oxide (FeP-rGO) has been reported as efficient electrocatalysts for OER under alkaline conditions. FeP nanoparticles require an overpotential of 290 mV @ 10 mAcm-2. It is well known that rGO is a good conductor and a support material for the catalysts. Hence, mixing of FeP nanoparticles with rGO has improved the catalytic efficiency further by reducing the overpotential to 260 mV to achieve 10 mAcm-2 current density4. The FeP nanoparticles and FeP-rGO composite showed the lowest overpotential at 10 mA/cm2 that has observed among the pnictide making these the most-efficient phosphide based OER catalyst till date. The hybrid catalyst showed a low Tafel slope of 50.8 mV/dec. The stability of the catalyst was excellent with 4h of continuous oxygen evolution and the catalytic activity was retained with a similar overpotential @ 10 mAcm-2. The synthesis of hybrid catalysts, detailed characterization, and electrochemical studies including liner scan voltammetry (LSV), choronoamperometry will be discussed in detail.