Laser-Printed Photoanode: Femtosecond Laser-Induced Crystalline Phase Transformation of WO₃ Nanorods for Space-Efficient and Flexible Thin-Film Solar Water-Splitting Cells

Despite its potential for clean hydrogen harvesting, photoelectrochemical (PEC) water-splitting cells face challenges in commercialization, particularly related its harvesting performance and productivity at an industrial scale. Herein, a facile fabrication method of flexible thin-film photoanode for PEC water-splitting to overcome these limitations, based on laser processing technologies, is proposed. Laser-induced graphene, a carbon structure produced through direct laser writing carbonization (DLWC), plays a dual role: a flexible and stable current collector and a substrate for the hydrothermal synthesis of tungsten trioxide (WO₃) nanorods (NRs). To facilitate water-splitting, a femtosecond-pulsed laser (fs laser) is focused on the WO₃ NRs, converting their crystalline phase from pristine orthorhombic to monoclinic structure without thermal damage. With NiFe layered double hydroxide (LDH) catalyst, the flexible thin-film photoanode exhibits good PEC performance (1.46 mA cm⁻² at 1.23 V_RHE) and retains ≈90% of its performance after 3000 bending cycles. With its excellent mechanical properties, the flexible photoanode can be operated in various shapes with different curvatures, enabling space-efficient PEC water-splitting by loading larger photoanode within a given space. This study is expected to contribute to the advancement of large-scale solar water-splitting cells, introducing a new approach to enhance H₂/O₂ production and expand its application range.