Cobalt Alloyed Catalyst Combined with Carbide and Carbon As Efficient Oxygen Evolution Reaction Catalysts for Alkaline Water Electrolysis

Abstract

Increasing demand for clean energy have triggered researches on alternative energy sources and devices to reduce use of fossil fuel. Hydrogen has been considered as one of the most promising energy source for future due to its high energy density and no air pollutant emission. Splitting water into hydrogen and oxygen is an environmentally friendly method for producing hydrogen gas. This technology can store excess electric energy in the form of chemical bonds of hydrogen, which can resolve an issue about surplus electric power of present renewable energy systems caused by irregular energy source such as airflow and sunlight. Water electrolysis reaction is divided into two half reactions; hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). High overpotential of both HER and OER is the most significant problems to hamper reaction rate and overall efficiency of water electrolysis, especially OER has much higher overpotential than HER. Therefore, recently major efforts have been devoted to exploring active catalysts for the OER in water electrolysis cell. Among many kinds of candidate materials for OER catalyst, cobalt (Co) and various Co based materials, including nanostructured Co3O4, CoSe2, Co based perovskites, CoP, CoB and Co/N-doped carbon, have drawn much attention for use in the alkaline water electrolysis system. These Co based catalysts have high OER activity in alkaline media comparable with precious metal based catalysts, such as IrO2 and RuO2. However, previous studies has focused mainly on the exploring desirable composites for low OER overpotential without careful mechanistic study. OER mechanism on Co based catalysts and descriptors for designing more efficient catalysts have been unclear yet. Herein, we tried to modify the electronic structure of Co through the strain effect. The strain effect modifies the adsorption energy of gaseous or ionic species for OER on Co surface that can be an effective way to design an active electrocatalyst. For making a strain in the Co lattice, we alloyed Co with other transition metals, such as iron (Fe), manganese (Mn), nickel (Ni), and combined with carbide and carbon through a facile solution based process. Graphitic carbon-nitride (g-C3N4) was used as a carbon source. Synthesized alloyed catalyst exhibited higher activity and durability for OER compared with Co and ruthenium dioxide (RuO2) catalysts in alkaline media (0.1 and 1 M KOH). And, the catalysts with tensile strain have much enhanced OER activity than compressive strained one.