Physical and Analytical Chemistry Seminar
Lecturer: Prof. Shane Ardo
Location: Faculty Seminar Room
Design strategies and mechanistic details of Photo…Chemical energy storage processes
Photo…Chemical energy storage occurs when photon energy is used to drive thermodynamically unfavorable chemical processes. Prototypical examples include water splitting, CO2 reduction, and N2 fixation, as well as non-redox-based reactions such as dialysis for generation of acid and base or desalination. My team is developing several classes of materials for Photo…Chemical processes, including solar photo-catalytic and photo-electro-chemical water splitting and new processes based on photo-iono-chemical energy conversion.1 Our expertise encompasses skillsets from several traditional disciplines, and includes electron microscopies, pulsed-laser spectroscopies, photoelectro-chemistries, numerical simulations, and molecular and materials syntheses.
Photo-catalytic H2 evolution: Particle suspension reactors for solar water splitting can generate H2 at a cost that is competitive with H2 produced by steam methane reforming.2,3 Motivated by this fact, my group recently proposed a dual-bed photocatalyst reactor with stacked photocatalyst beds (Figure 1),4,5 which enables increases in efficiency due to serial light absorption5,6 and short redox shuttle mass transport distances.5 Using numerical models, we simulated that a 10% solar-to-hydrogen conversion efficiency is possible in the absence of convection,5 and that natural convection further enhances performance. We also discovered that reactor efficiencies can increase when an ensemble of optically thin materials replaces the standard planar light-absorber geometry.7 We are leveraging these computational discoveries to experimentally advance the performance of best-in-class materials for photocatalytic water splitting, such as doped SrTiO3, BiVO4, and WO3.
Photo-iono-chemical desalination: Protonic (H+) processes that occur in water in the dark are identical to electronic (e–) processes that occur in semiconductors in the dark; for this reason, my team defines water a protonic semiconductor. Using this fact, over a half-century ago Prof. John Bockris demonstrated that hydrated ion-selective polymer membranes can form ionic diodes. Recently, my team coupled this discovery with photoacid dye sensitization to demonstrate photo-ionochemical energy conversion and photovoltages in excess of 100 mV.1,8,9 We observed that this photo-iono-chemical phenomenon is general in that covalent modification of several polymer scaffolds with several photoacid dye molecules each resulted in a photovoltaic response.1 These photo-responsive polymers form a new class of functional materials that upon optical excitation result in changes in ion concentrations and electrostatic potentials, which we plan to use to drive redox reactions and desalination (Figure 2), as well as biological cellular events.
(1) S Ardo, …, PCT International Patent Application, 2018, US20180065095 A1.
(2) S Ardo, … (45 total co-authors), Energy & Environmental Science 2018 11 2768.
(3) BA Pinaud, … S Ardo, … TF Jaramillo, Energy & Environmental Science 2013 6 1983.
(4) DM Fabian, … S Ardo, Energy & Environmental Science, 2015, 8, 2825, 10.1039/c5ee01434d.
(5) R Bala Chandran, … S Ardo, and AZ Weber, Energy & Environmental Science 2018 11 115.
(6) S Keene, … S Ardo, Energy & Environmental Science 2019 12 261.
(7) S Keene and S Ardo, Nature Materials under review.
(8) W White, … S Ardo, Journal of the American Chemical Society 2017 139 11726.
(9) W White, … S Ardo, Joule 2018 2 94.