Fabrication of CuInS2 photocathodes on carbon microfiber felt by arc plasma deposition for efficient water splitting under visible light
An efficient copper indium disulfide (CuInS2) photocathode was fabricated on conductive carbon microfiber felt (CMF), which comprises a three-dimensional (3D) network of carbon fibers (CFs), by the sequential deposition of metal precursors (Cu and In) and subsequent annealing under a stream of diluted H2S. Although the conventional electrochemical deposition method failed to deposit the metal precursors homogeneously on the CMF, the arc plasma deposition (APD) method did so successfully. The unique features of the APD method enabled superior homogeneity of the Cu/In ratio throughout the CMF, not only on the outer surface, but also inside the 3D network, under optimized conditions. Another unique feature of the APD method is its ability to deposit metal species on the back surface of the CFs, thus allowing an almost full-coverage coating of the 3D structure of the CMF substrate. The as-prepared CuInS2/CMF photocathode was further modified with a thin layer of CdS and Pt particles, and then used for photoelectrochemical (PEC) water reduction under visible light. The modified Pt–CdS/CuInS2/CMF photocathode exhibited relatively high incident photon-to-electron conversion efficiency (IPCE) values (ca. 40% at 0 V vs. the RHE under 600 nm) and higher cathodic photocurrent density under continuous visible-light irradiation (λ > 400 nm) than a conventional Pt–CdS/CuInS2 cathode fabricated on a two-dimensional molybdenum substrate. PEC water reduction proceeded stably over the Pt–CdS/CuInS2/CMF photocathode under visible light with almost 100% faradaic efficiency, indicating that CMF is a promising photocathode substrate for PEC water splitting.