In this work we report the production of nanostructured WO3 photoanodes for solar water splitting produced via anodisation using for the first time citric acid (CA), a safer and more environmentally friendly alternative to fluoride-based electrolytes. Photoelectrochemical solar water splitting has shown potential as a renewable method for hydrogen production, a key ingredient to advance the de-carbonisation of our economy. Many methods to produce WO3 photoanodes are time-consuming and require high temperatures and/or toxic chemicals, such as fluoride-based electrolytes. Here we report on a systematic investigation of the anodisation of tungsten using CA to establish a relation between (i) anodisation parameters (current, time and electrolyte), (ii) the resulting nanostructured morphology and (iii) its performance as a photoanode for water splitting. Characterisation was carried out by X-ray diffraction, scanning electron microscopy, linear sweep voltammetry, and ultraviolet-visible spectroscopy. After optimisation, the obtained WO3 photoanodes produced a photocurrent of 0.88 mA cm-2 at 1.0 V vs. Ag/AgCl in 0.5 M aqueous H2SO4 under AM1.5 solar irradiation. At low applied potentials (below 0.67 V vs. Ag/AgCl), closer to practical conditions, the photoanodes produced in CA outperformed a conventional counterpart made using a NH4F electrolyte. The CA-anodised photoanodes also showed higher stability, retaining 90% of their activity after 1 h of chopped solar illumination. This work demonstrates the promise of anodisation in citric acid as an efficient and more sustainable method for the production of WO3 photoanodes for solar water splitting.
ASJC Scopus subject areas
- Chemical Engineering(all)