Novel Electrocatalysts for Generating Oxygen from Acid Water Electrolysis

Rapidly increasing global energy demand and developing carbon-neutral economy impose great challenge to the scientific community and it requires untiring efforts to exploit and store abundant but diffuse renewable energy sources. One innovative and promising approach for that is the efficient production of hydrogen serving as fuel, through electricity-driven water splitting. However, the overall efficiency of the reaction is largely impeded by the kinetically sluggish oxygen evolution reaction (OER), imposing serious overpotential requirement. Therefore, an efficient oxygen evolution catalyst is essential to enhance the reaction rate and/ or lower the overpotential. Although precious metal oxides, such as RuO2 and IrO2, are considered to be the most active OER electrocatalysts, they are not suitable for large-scale applications because of their scarcity and high costs. So There is an ongoing interest to find earth-abundant and inexpensive electrocatalysts for OER. In response, non-noble transition-metal-based oxides, layered double hydroxides (LDH), perovskite-type metal oxides are some of the advance electrocatalyst candidates with their own limitations.

Here, for the first time, we focus on layered transition metal dicalchogenides (TMDs) like MoS₂ and TaS₂ in this search due to their natural abundance and high activity towards hydrogen evolution. We report MoS₂ and TaS₂, in both their 2H and 1T polymorphs that display excellent catalytic activity for OER in much required acid medium. They are chemically exfoliated to thinner nanosheets from MoS₂ precursor and TaS₂ nanostructures synthesized by chemical vapour deposition. Structural and electrochemical studies reveal their corresponding semiconducting 2H and metallic 1T polymorph and the impressive electrocatalytic performance respectively. The proliferation of active sites is such a high for those materials that an electrocatalytic current density of 10 mA cm⁻² is achievable with overpotential much lower than that of the benchmark IrO₂ or RuO₂OER catalyst. The Tafel slopes found for the different samples are also in good rivalry of the benchmark catalyst. The performances are also analyzed on the basis of their probable structure relation.

This work presents general strategies to grow nanostructures of layered TMD materials for the enhanced catalytic performance in OER and open up a new avenue in the pursuance of water splitting research towards the growth of hydrogen economy.