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

Abstract 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.