Every major change in the living standard for humanity has had an energy revolution at its heart. The energy demand, primarily from emerging economies, will double by 2050. The countervailing urgency of the threat of climate change requires a major shift in our energy sourcing. Amongst renewable energy options, the conversion of sunlight into stored chemical fuels is particularly attractive. Research aimed at the efficient utilization of solar energy is inherently interdisciplinary, involving inorganic and organic synthesis, solid state chemistry and physics, electrochemistry, chemical kinetics and mechanism, and theoretical and computational chemistry. The National Science Foundation Center for Chemical Innovation in CCI Solar Fuels, established in 2008 and renewed in 2013, brought together leading experts in chemistry and chemical engineering from 15 universities to focus on a grand challenge - the efficient, solar-driven conversion of water to H₂ and O₂. Research focused on three primary areas: development of enhanced light absorbers; discovery of optimized catalysts; and integration of components into functional assemblies.

We employed Pulsed Laser Plasma (PuLP) synthesis to produce new catalytic materials for water splitting. Efficiency can be improved by maximizing surface area through reduction in particle size, with the additional benefit of modulation of electronic properties through quantum confinement. Since we discovered Ni₂P as an acid-stable, earth-abundant catalyst for the Hydrogen Evolving Reaction (HER) catalyst in 2013, transition metal phosphide HER catalysts have become mainstream for various energy-related applications. Our efforts involved developing new synthetic routes to previously inaccessible classes of nanoparticles, methods to evaluate bulk powders, single crystals, and ingots of refractory materials. We developed BiVO₄-based photoanodes for PhotoElectrochemical Cells (PECs) by tuning morphology and composition to enhance photon absorption and electron-hole separation. We also performed experimental and theoretical investigations that led to an understanding of the BiVO₄/Oxygen Evolution Catalyst (OEC) interfaces and the factors responsible for enhanced chemical and photoelectrochemical stabilities. We established and validated a method to quickly screen a variety of OECs using O₂-sensitive fluorescence quenching. Two combinations stood out as exhibiting the highest Oxygen Evolving Reaction (OER) activity: oxides composed of Ni:Fe:Al in 2:1:2 and 3:1:1 stoichiometries. We developed an elegant technique for detecting liberated O₂ based on microwave rotational spectrum of dioxygen in a magnetic field, which is incredibly sensitive to minute amounts of oxygen. We discovered the Reactive Interface Patterning Promoted by Lithographic Electrochemistry (RIPPLE) technique for facile periodic and quasi-periodic deposition of metal oxides on Si in nanostructured patterns at mesoscopic length scales over large areas of conductive substrates. This method allowed us to interface catalysts to light absorbing/separating materials. Oxidation resistant ligands are required for oxidizing functional groups such as metal oxos. We developed the fundamental synthetic chemistry of two classes of oxidation-resistant ligands: macrobicyclic hexacarboxamides and metaphosphates. We developed Surface Interrogation Scanning ElectroChemical Microscopy (SI-SECM), which we used for direct quantification and time-resolved detection of surface-active sites and intermediates for HER and OER catalysts. We used computational methods to generate free energy diagrams and identify thermodynamically favorable pathways, fundamental mechanisms, and key intermediates for NiFe oxyhydroxide and other catalysts. We studied the performance of charge transport limited semiconductors by increasing incident light absorption and electrochemically active surface area in nanostructured light absorbers. We developed bipolar membranes that sustain pH gradients and efficiently dissociate water in electric fields. We developed soft contact probe techniques and showed that Schottky resistance can be reduced through the formation of microrods with highly doped bases or surface modification for conducting polymer contacts. We developed dielectric-dependent hybrid functionals for accurate calculations of band gaps, as well as band level alignment at surfaces and optical transition energies in defective oxides, including wide gap oxide semiconductors and transition metal oxides.

Our outreach programs - Solar Energy Activities Lab (SEAL), Juice-from-Juice (JfJ), Heterogeneous Anodes Rapidly Perused for Oxygen Overpotential Neutralization (HARPOON), and Informal Science Education – impacted teachers and over 10,000 students from middle schools, high schools, and colleges. We focused on diversity and inclusion to under-resourced communities in Southern California and Puerto Rico. We collaborated with other CCIs and participated in diversity conferences including Society for Advancement of Chicanos/Hispanics and Native Americans in Science (SACNAS) and National Organization for the Professional Advancement of Black Chemists and Chemical Engineers (NOBCChE).

Last Modified: 11/03/2019
Modified by: Harry B Gray