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Sulfur-doped cobalt oxide (S-Co 3 O 4) crystals exhibit excellent catalytic activities towards multiple useful reactions, however, the impact of the structural properties on the resultant catalytic activities has been overlooked in the past. We demonstrate a facile vaporphase hydrothermal (VPH) doping approach to effectively create electrocatalytically active surface sulfur species on the chemical bath deposited polycrystalline Co 3 O 4 nanowires for iodine reduction reaction (IRR). The dye-sensitized solar cells (DSSCs) equipped with the S-Co 3 O 4 nanowire film as the counter electrode (CE) achieve a best energy conversion efficiency of 6.78%, which is comparable to those of DSSCs with commercial Pt CE (7.36%). The impact of film structure, VPH temperature and VPH duration on the resultant structures as well as the electrocatalytic activities has been comprehensively studied. More importantly, our results manifest a close correlation between the surface sulfur dopant level and the key electrocatalytic activity indicators. The VPH approach could be further extended to the fabrication of low-cost, high-performance nanomaterials for energy conversion applications.

Metal chalcogenide related materials have demonstrated outstanding catalytic activities for numerous chemical reactions in energy conversion devices. However, the actual active species have not yet been fully identified, especially for triiodide reduction in dye-sensitized solar cells (DSSCs). We herein adopted a vapor-phase hydrothermal (VPH) approach to controllably create the sulfur dopants on the Co 3 O 4 nanosheets surface for high-performance DSSCs with a best power conversion efficiency (PCE) of 8.86%. More importantly, our XPS and electrochemical analysis confirm a close correlation between the S 2species and the electrocatalytic activities.

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