Boron nitride photocatalysts for solar fuel synthesis

Reshaping our global energy portfolio in light of the rising anthropogenic CO2 emissions is paramount. Solar fuel production via photocatalysis constitutes a sustainable energy generation route, allowing one to harness the abundance of sunlight for CO2 transformation. In this thesis, we develop a new materials platform for boron nitride (BN) photocatalysts in solar fuel synthesis. We present a proof-of-concept for a porous boron oxynitride (BNO) photocatalyst facilitating gas phase CO2 capture and photoreduction, without doping or cocatalysts. We then present two routes to enhance light harvesting and photoactivity in BN: boron- and oxygen doping. Boron doping yielded B-BNO, the first water-stable, photoactive BN material, facilitating liquid phase H2 evolution under deep visible irradiation (λ > 550 nm) and gas phase CO2 photoreduction. In parallel, we demonstrate that tuning the oxygen content in BNO can lower and vary light harvesting to the deep visible region. Using a systematic design of experiments process, we tune and predict the chemical, paramagnetic and optoelectronic properties of BNO. We probe the role of free radicals and paramagnetic states on the photochemistry of BNO using a combined experimental, computational and first-principles approach. The family of BN photocatalysts all exhibit unique paramagnetism, shown to arise from free radicals in isolated OB3 sites, which we unequivocally confirm as the governing state for red-shifted light harvesting and photoactivity in BNO. Finally, we explore a new avenue in BN photocatalyst design and present the first example of semiconducting BNO quantum dots for CO2 photoreduction. The evolution rates, quantum efficiencies, and selectivities of all the BN materials surpassed P25 TiO2 and graphitic carbon nitride - benchmark photocatalysts in the field. Overall, this thesis opens the door to a radically new generation of BN-based photocatalysts for solar fuels synthesis.Open Acces