Yuanbing Mao1

1, The University of Texas at Rio Grande Valley, Edinburg, Texas, United States

The exploration of new materials and/or structures as efficient electrodes for industry-level photoelectrochemical (PEC) water splitting into usable H2 fuel has attracted intense interest from the whole world. As an advanced intelligent tactic, assembling nano-building blocks into desirable structures with new hierarchy and scaling-up laws has been explored to achieve high performance and functionality. In terms of methodology, a seeding method in solution phase still confronts some engineering obstacles notwithstanding it being regarded as a major avenue to fabricate heterogeneous nanostructures of semiconductors. To elevate the spatial occupancy of one-dimensional ZnO nanostructures and overcome the limitations of multistep seeding method currently widely used, we have developed a facile procedure with high yield to fabricate “caterpillar-like” ZnO nanostructured network (CZN) for photoelectrochemical applications. Moreover, by fine-tuning the synthesis procedure and manipulating their growth process, the dependence of their photoelectrochemical properties on geometry factors of the unique CZN consisting of branched ZnO nanowires onto ZnO nanofibers with tunable surface-to-volume ratio and roughness factor has been investigated. They offer mechanically and electrically robust interconnected networks with open micrometer-scale structures and short hole diffusion length. The preferential light-material interaction and charge separation to maximize the photo-to-hydrogen conversion efficiency were further studied. When used as photoanode, our CZN not only favors sunlight harvesting with multireflection ability, but also suppresses the recombination of photogenerated charge. Compared to the literature results, our CZN photoanodes with ZnO nanobranches of ~2.2 μm in length and ~25 nm in diameter exhibited the highest photocurrent density of 0.72 mA/cm2 at +1.2 V (versus Ag/AgCl) and conversion efficiency of 0.209% at +0.91 V (versus RHE) without being decorated with noble metal cocatalysts or nonmetallic/metallic dopants due to their favorable structural features. Overall, our procedure to obtain the desirable CZN provides great opportunities for facile and efficient fabrication of model photoelectrochemical anodes and would be applied to other materials for sustainable chemistry and engineering applications.