(348e) Layered - Hyperthin Electrocatalysts for the Water Splitting Reactions

We report scalable, solution-processing methods for synthesizing two different layered hyperthin nanostructure electrocatalysts for the water splitting reactions. First, we show that 2D FeS₂ disc nanostructures are an efficient and stable hydrogen evolution electrocatalyst. By changing the Fe:S ratio in the precursor solution, we were able to preferentially synthesize either 1D wire or 2D disc nanostructures. The 2D FeS₂ disc structure has the highest electrocatalytic activity for the hydrogen evolution reaction, comparable to platinum in neutral pH conditions. The ability of the FeS₂ nanostructures to generate hydrogen was confirmed by scanning electrochemical microscopy (SECM), and the 2D disc nanostructures were able to generate hydrogen for over 125 h. Second, we report a novel solution-processing synthesis route for creating nickel-iron oxyhydroxides. Nickel-iron oxyhydroxides are non-precious metal electrocatalysts for the oxygen evolution reaction (OER) that have high efficiency in alkaline media. It has been proposed that the layered structure of the oxyhydroxide allows for electron hole transport from the bulk material to the solution interface, which creates very high active site densities. We compared the intrinsic electrocatalytic activity and active site densities for two Ni_0.8:Fe_0.2 oxyhydroxides with similar electrochemical surface areas (ECSA) â?? one synthesized via electrochemical conditioning of crystalline Ni_0.8:Fe_0.2 oxide and the second synthesized via our new solution-processing route. The overpotential for oxygen evolution on Ni_0.8:Fe_0.2 oxyhydroxide decreased from 366 mV on the crystal-derived structure to 268 mV on the new solution-processing structure at 1 mA cm^-2 when normalized to the ECSA of the catalyst. We measured the active site density of both Ni_0.8:Fe_0.2 oxyhydroxides directly using the surface interrogation mode of scanning electrochemical microscopy (SI-SECM).