Tungsten carbide-nitride on graphene nanoplatelets as a durable hydrogen evolution electrocatalyst.

Alternatives to platinum-based catalysts are required to sustainably produce hydrogen from water at low overpotentials. Progress has been made in utilizing tungsten carbide-based catalysts, however, their performance is currently limited by the density and reactivity of active sites, and insufficient stability in acidic electrolytes. We report highly active graphene nanoplatelet-supported tungsten carbide-nitride nanocomposites prepared via an in situ solid-state approach. This nanocomposite catalyzes the hydrogen evolution reaction with very low overpotential and is stable operating for at least 300 h in harsh acidic conditions. The synthetic approach offers a great advantage in terms of structural control and kinetics improvement.

Efficient water oxidation with organometallic iridium complexes as precatalysts.

Catalytic water oxidation has been investigated using five iridium complexes as precatalysts and NaIO4 as an oxidant at various pH conditions. An increase in the activity of all complexes was observed with increasing pH. A detailed analysis of spectroscopic data together with O2-evolution experiments using Cp*Ir(6,6'-dihydroxy-2,2'-bipyridine)(OH2)(2+) as a precatalyst indicate that the high catalytic activity is closely connected with transient species (A) that exhibits an absorption band at λmax 590 nm. The formation of this active form is strongly dependent on reaction conditions, and the species was distinctly observed using a small excess of periodate. However, another species absorbing at 600 nm (B), which seems to be a less active catalyst, was also observed and was more prominent at high oxidant concentration. Dynamic light scattering analysis and transmission electron microscopy have identified species B as 120 nm nanoparticles. The ultrafiltration method has revealed that species A can be attributed to particles with size in the range of 0.5­2 nm, possibly small IrOx clusters similar to those described previously by Harriman and co-workers (J. Phys. Chem., 1991, 95, 616­621).