Towards sustainable TiO2 photoelectrodes based on cellulose nanocrystals as a processing adjuvant†

Abstract

Photoelectrodes of TiO₂ in the form of films are commonly fabricated using screen printing techniques, employing viscous commercial TiO₂ pastes. However, these pastes comprise environmentally unfriendly, multicomponent formulations designed to manufacture the photoactive TiO₂ nanoparticles. To strive for sustainable processing and pave the way for the use of liquid-phase film processing technologies, the inherent limited water dispersibility of TiO₂ nanoparticles must be overcome. In this study, we show that cellulose nanocrystals, produced via an environmentally benign one-pot hydrolysis process, enable the preparation of stable TiO₂ water dispersions. The remarkable stability of these dispersions, evidenced by their outstanding ξ-potential values of −34 mV, facilitates the fabrication of macroporous TiO₂ photoactive films throughout spray coating. Employed as photoanodes in a photoelectrochemical cell, our TiO₂ photoanodes are compared with conventional TiO₂ electrodes obtained from commercial pastes under water splitting conditions. Interestingly, our photoanodes reveal a remarkable three-fold enhancement of the photocurrent performance (132 vs. 46 μA cm⁻²) and a four-fold increase in the on–off response rate (4 vs. 1 s). These findings underscore the valuable role of cellulose nanocrystals as a green processing asset for achieving TiO₂ water dispersions. Moreover, they serve as sacrificial adjuvants for preparing highly macroporous and functional film photoelectrodes, representing a significant step forward in the pursuit of sustainable and efficient materials processing.