More Photocatalysis With Less Light in Polar Semiconductors-The Role of Pyroelectric Fields

Photocatalysis is an energy conversion process, where its efficiency is expressed as the ratio of formed or broken bond energy to solar energy. While the light-induced charge transport behind photovoltaics and photocatalysis is the same, photocatalysis includes the additional step of adsorption/desorption. For the case of wastewater remediation, the conversion efficiency from solar-to-chemical energy is several orders of magnitude lower than photovoltaic. This underlines that the light-induced charge transport is not the rate-limiting step of photocatalysis and thus its optimization has very limited potential. Here, we present the case where modulated solar irradiation removes approximately 50% of photons compared to continuous irradiation, and still achieves an increase in photocatalytic performance. This overcompensation originates from the effect of pyroelectric fields from the polar BaTiO₃ near the phase transition. Interestingly, it is not the absorption of the catalyst that triggers the relevant temperature changes but the absorption of IR radiation through water. Using methyl orange and rhodamine B as model pollutants and BaTiO₃ nanoparticles as a photocatalyst, we demonstrate the proof of concept and provide quantitative consistency as a function of particle size that governs the phase transition temperature, as a function of offset temperature to approach the phase transition, and through control experiments without IR contributions.