Controlled growth of MoO2 nanowires and nanosheets by chemical vapor deposition: a comparative study of their electrochemical water splitting performance

MoO 2 is a promising material for efficient and cost-effective electrocatalytic water splitting, particularly for the oxygen evolution reaction (OER) in alkaline media. Modifying the morphology, composition, or oxidation state of MoO 2 can enhance its active surface area and performance. In this study, Mo-coated carbon paper was used as a substrate to synthesize well-organized MoO 2 nanowires and nanosheets via a one-step CVD method without any catalyst. The nanosheets and nanowires grow perpendicularly to the substrate. MoO 2 nanowire arrays exhibit superior OER performance, characterized by a lower onset potential (1.54 V), a smaller Tafel slope, and enhanced durability compared to nanosheets. This improvement is likely attributed to the increased number of exposed active sites, reduced presence of oxidized Mo 4+ , and smaller crystalline size. Graphical abstract Here, well-organized MoO 2 nanowires and nanosheets have been fabricated on carbon paper using a one-step CVD method by reducing MoO 3 with Mo powder to investigate the intrinsic relationship between morphology, elemental composition and state, and their electrocatalytic properties. The obtained nanosheets presented as a flower-like structure, while nanowires formed into well-aligned arrays. MoO 2 nanowires contained higher amounts of Mo 4+ , were composed of smaller crystal grains, and possessed a lower onset potential for OER (oxygen evolution reaction) at about 1.54 V, a smaller Tafel slope at about 110 mV/dec, and better durability when compared to MoO 2 nanosheets.