Spectroscopy-led Development of Organic Photocatalysts for Sustainable Energy Production

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Renewable solar energy needs to be paired with energy storage to overcome the hourly mismatch between solar energy supply and energy demands. Inspired by the natural photosynthesis of plants, solar energy can be stored in high-density chemical bonds. Solar fuels - high energy molecules generated from sunlight - can be produced by photocatalysts that drive water splitting (to make H2) or photoreduction of CO2 (to make liquid fuels). To accelerate the transition to a low-carbon society, cost-effective photocatalysts that produce solar fuels with improved efficiencies must be developed. Carbon nitride (CNx) has emerged as a leading cost-effective photocatalyst. CNx can be synthesized by simple heat treatment of inexpensive molecules and has the requisite (photo)chemical stability. High photocatalytic efficiencies (quantum yields up to 50%) for H2 photogeneration have been demonstrated using sacrificial oxidation substrates. To close the sustainable solar fuel cycle, these substrates must be replaced with H2O, the product generated when energy is released. However, H2O oxidation is more challenging. The resulting solar-to-fuel efficiency < 1% is far from the targeted commercialization barrier of 10%. My research program will develop the structure-activity relationships needed to engineer superior photocatalysts. The advanced spectroscopic technique of transient absorption spectroscopy (TAS) will shed light on the photophysics of CNx and identify the most crippling efficiency bottlenecks. The impact of energetic, structural and spatial heterogeneities on photoefficiency is poorly understood. To gain a holistic view of the key processes that determine photoactivity, my group will investigate the charge carrier dynamics of CNx modified on three different axes: (nano)morphology, chemical nature of terminal groups, and deposited redox cocatalysts. To uncover spatial heterogeneities in CNx, I will develop microsecond - second transient absorption microscopy (TAM) to map out processes such as charge trapping, charge accumulation and interfacial charge transfer. Spectroscopy will yield crucial photophysical and structural insights needed to direct synthetic modifications of photocatalysts. The synergistic spectroscopic and synthetic approach will optimize CNx morphology and internal photophysics, required for both efficient H2 production and CO2 photoreduction. My long-term vision is to take advantage of the optimized CNx photophysics to develop solar-driven carbon capture and utilization, using CNx and light to sequester CO2 within materials with long lifespans. HQP involved in the research program will gain a unique combination of synthetic, spectroscopic, communication, and management skills that make them attractive to the growing clean technology sector. HQP will contribute to the clean energy sector and the important H2 industry that will surpass US$200 Bn by the end of 2025, developing Canada's economy and helping reach lower CO2 emissions targets.