This journal is © The Royal Society of Chemistry and the Chinese Chemical Society 2017 Mater. Chem. Front., 2017, 1, 65--72 | 65 Cite this: Mater. Chem. Front., 2017, 1, 65 Nanofiber-supported CuS nanoplatelets as high efficiency counter electrodes for quantum dot-based photoelectrochemical hydrogen production† F. Navarro-Pardo,‡ a L. Jin,‡ a R. Adhikari, a X. Tong, ab D. Benetti, a K. Basu, a S. Vanka, c H. G. Zhao,* a Z. T. Mi, c S. H. Sun, a V. M. Castano, d A. Vomiero* e and F. Rosei* af We developed a hierarchically assembled hybrid counter electrode (CE) based on copper sulfide (CuS) nanoplatelets grown on polymer nanofibers. The resulting CE was used in a quantum dot (QD)-based photoelectrochemical (PEC) system for H 2 generation in the presence of sacrificial agents (S 2À /SO 3 2À ). The concept is to increase the specific surface area of the CE, aiming at maximizing charge exchange at the electrode, which boosts efficient generation of H 2 and to obtain a stable structure for long-term operation of the device. Structural and morphological characterization indicated the presence of a covellite crystalline phase (CuS). PEC tests showed that the CuS nanoplatelets grown in the CEs could replace Pt CEs in either visible-active or near infrared (NIR)-active QD-based PEC systems. Specifically, saturation of the photocurrent density (B7.5 mA cm À2 ) occurred at B0.6 V versus the RHE, when using a NIR QD-based TiO 2 photoanode and a nanofiber-supported CuS as the CE. Stability tests of the nanofiber-supported CuS CE showed that 85% of the initial photocurrent density was maintained after B1 h, which is similar to that obtained with the Pt foil CE (86%). In contrast, CuS nanostructures directly deposited on FTO glass without nanofibers (CuS/FTO CE) exhibited poor stability. CuS/FTO CE degraded quickly, showing a 90% drop in the initial photocurrent within 200 s testing whereas a 14% drop in the initial photocurrent was observed for the Cu x S on brass within 10 min of testing. Our new nanofiber supported-CuS CE stands out due to its higher performance compared to brass and its similar stability compared to Pt during long term PEC operation. Additionally, our hybrid CE showed a better catalytic performance than the Pt CE and good stability in cyclic voltammetry tests. These results demonstrate that the nanofiber-supported CuS is a promising cost effective alternative to Pt as a highly efficient CE for PEC H 2 generation. Introduction Hydrogen (H 2 ) as a clean fuel combines the advantages of high energy storage density, ease of transportation, cost-effectiveness and the generation of water as the only byproduct of its use for power generation. 1 Photoelectrochemical (PEC) H 2 production represents a clean and environmentally sustainable approach to provide abundant energy. Generally, a PEC cell presents reduction–oxidation (redox) reactions driven by electron–hole pairs created by incident photons, namely, the holes oxidize the water/hole scavenger at the surface of an anode, and electrons migrate to the counter electrode (CE) to reduce water and produce H 2 . 2–5 An integrated PEC system has three main components: a photoanode, an electrolyte and a CE. 6 Quantum dot (QD)-sensitized photoanodes have recently attracted much attention, because of their excellent optical activity in a broad spectral range as well as the fast exciton dissociation and a Centre for Energy, Materials and Telecommunications, Institut National de la Recherche Scientifique, 1650 Boul. Lionel-Boulet, Varennes, QC, Canada J3X 1S2. E-mail: zhaoh@emt.inrs.ca, rosei@emt.inrs.ca b School of Chemistry and Material Science, Guizhou Normal University, Guiyang 550001, China c Department of Electrical and Computer Eng., McGill University, 3480 Univ. Str. W, Montreal, QC, Canada H3A 0E9 d Centre of Applied Physics and Advanced Technology, National Autonomous University of Mexico, 3001 Boul. Juriquilla, Juriquilla, Santiago de Queretaro, 76230, Mexico e Division of Engineering Sciences and Mathematics, Luleå University of Technology, 971 98 Luleå, Sweden. E-mail: alberto.vomiero@ltu.se f Institute for Fundamental and Frontier Science, University of Electronic Science and Technology of China, Chengdu, 610054, P. R. China † Electronic supplementary information (ESI) available: See DOI: 10.1039/c6qm00144k ‡ These authors contributed equally to this work. Received 27th July 2016, Accepted 6th October 2016 DOI: 10.1039/c6qm00144k rsc.li/frontiers-materials MATERIALS CHEMISTRY FRONTIERS RESEARCH ARTICLE Published on 24 October 2016. Downloaded on 15/12/2016 22:25:32. View Article Online View Journal | View Issue