Characterization of n-Type Semiconducting Tungsten Disulfide Photoanodes in Aqueous and Nonaqueous Electrolyte Solutions

Synthetic, single crystal, n‐type semiconducting has been characterized as a photoanode in aqueous and nonaqueous electrolyte media. The was synthesized from the elements by bromine and chlorine transport to yield plates up to in dimension. Interface characterization includes ( i ) cyclic voltammetry in the presence of a large number of fast, one‐electron redox couples in solutions; ( ii ) steady‐state photocurrent‐voltage properties in aqueous and nonaqueous solutions of ; ( iii ) tests of durability; ( iv ) wavelength dependence of photocurrent and photovoltage; and ( v ) high resolution (∼5 μm) laser mapping of the surface to reveal surface inhomogeneity with respect to output photovoltage. Highlights of the results are: ( i ) n‐type is durable in aqueous electrolytes containing high concentrations of to yield efficient visible light‐assisted oxidation of ; e.g. , has up to 6.9% and up to 12% efficiency at a 632.8 nm input power of 16 mW/cm 2 ; ( ii ) in aqueous, but not nonaqueous, solutions I − adsorbs such that the onset of photocurrent is shifted several hundred millivolts as for other metal dichalcogenide photoanodes; the shift is sufficient that visible light can be used to sustain the conversion of to and with no other energy input; ( iii ) cyclic voltammetry in for a number of redox couples shows that a photovoltage of up to ∼0.7V is possible; photovoltage varies from 0.0 to ∼0.7V for redox couples having from ∼0.0V vs. SCE to ∼+0.8V while the photovoltage is fixed at ∼0.7V for more positive than ∼+0.8V vs. SCE; ( iv ) efficiency for halogen generation in aqueous solutions generally exceeds efficiency in solutions; and ( v ) the diffusion length of holes parallel to the surface is ∼200 μm which explains the dramatic influence of the steps on the recombination of carriers on layered compounds.