Developing photocatalysts capable of organic oxidations enables the generation of value-added products from biomass feedstocks through visible light irradiation. Through a series of nonaqueous photocatalytic experiments, we have uncovered that CdS nanowires catalyze benzyl alcohol (BnOH) oxidation and 5-hydroxymethylfufural (HMF) oxidation. The rate can be improved by introducing nitrate salts that act as a redox mediator in solution. Specifically, nitrate salts of lithium, magnesium, calcium, and manganese promote the selective photooxidation of BnOH to benzaldehyde on CdS in 70–100% yields at rates up to 13.6 mM h–1, compared to 8% yield at 3 mM h–1 in the absence of a nitrate mediator. Kinetic analysis reveals that, in the absence of nitrate salts, the reaction is first-order with respect to BnOH, while in the presence of nitrate, the reaction is half-order in BnOH. This rate law disparity, along with radical trapping and kinetic isotope experiments, suggests that nitrate-mediated alcohol oxidations proceed through a mechanism involving the catalytic generation of a nitrate radical, NO3 •. The generation of this radical also enables the selective photooxidation of HMF to 2,5-diformylfuran at a rate of 2.6 mM h–1 using CdS nanowires.

Tungsten oxide (WO 3 ) electrodes were synthesized by spin-coating an ammonium metatungstate sol. Instability in photocurrent during water oxidation applications has previously been attributed to formation of destructive peroxide intermediates. Under constant illumination, repeated cycles of poising WO 3 electrodes at 0.98 V vs Ag/AgCl in pH 1 sulfate solution followed by measuring the open-circuit potential for several hours show reversibility in the photocurrent decay. This behavior is attributed to photochromic H x WO 3 generated at low concentration within the electrode, which serves to increase the donor density. The Mott−Schottky analysis of electrochemical impedance spectroscopy measurements on WO 3 electrodes before and after performing the oxygen-evolution reaction (OER) exhibits a decrease in donor density from 2.8 × 10 22 to 6.0 × 10 21 cm −3 with a corresponding 110 mV positive shift in the flat-band potential, indicative of tungsten oxidation during the OER. Tungsten oxidation is corroborated by a decrease in W 5+ signal in the X-ray photoelectron spectroscopy data. Measuring the OER rate by gas chromatography during water oxidation shows concurrent recovery of catalytic activity after resting at open circuit under illumination, illustrating the key role of H x WO 3 during photoelectrocatalysis.

A series of asymmetric iron(II) dichloride and dicarbonyl pyridinediimine (PDI) complexes that contain either pendant Lewis bases or Lewis acids located in the secondary coordination sphere were synthesized. These complexes are important intermediates in the reduction scheme of the small molecule CO2 on iron(II). The electrochemistry of the direduced FePDI(CO)2 complexes was evaluated for the 2‐electron oxidation from the reduced‐ligand to the neutral‐ligand species. The complexes with either pendant Lewis bases or Lewis acids located in the secondary coordination sphere displayed reduction potentials for CO release that span over 300 mV.

Nitrate anion (NO3 –) oxidation to nitrate radical (NO3 •) is chemically irreversible in acetonitrile (MeCN) solvent due to solvent-based hydrogen-atom transfer (HAT). Introducing benzyl alcohol (PhCH2OH) leads to competition with MeCN for electrochemically generated NO3 • and affords benzaldehyde (PhCHO) product with ∼80% faradaic efficiency (FE) in 250 mM PhCH2OH. Stoichiometric HNO3 forms during HAT reactions (observed by UV–vis spectroscopy) and exists as an electrochemically inert and weak electrolyte; this off-cycle form of nitrate can be reintroduced to the catalytic cycle upon deprotonation by 2,6-lutidine while maintaining the base-free FE. Oxygen reduction complements nitrate oxidation during catalysis and reduced oxygen species (ROS) generated during proton-coupled oxygen reduction are identified through rotating ring-disk electrochemistry; proton-coupled oxygen reduction indicates ROS are capable of rendering NO3 – catalytic when collocal. Directly observing ROS as the stoichiometric base generated during nitrate anion oxidation resolves differences in photocatalytic vs photoelectrochemical reactivity of NO3 – in base-free conditions and points toward HAT as the general mode of reactivity for nitrate radical in acetonitrile solutions.

A comparison of photoelectrochemical oxygenevolution reaction (OER) and chloride oxidation is performed on semiconducting H x WO 3 thin films. Over a 3 h controlled potential coulometry (CPC) experiment, the photocurrent density recorded during OER in a nitrate electrolyte decreases to half the starting photocurrent. However, if the same electrolysis experiment is performed with a chloride electrolyte, the photocurrent density is much more stable, degrading by only 5% over the same period. Linear sweep voltammetry (LSV) in the nitrate electrolyte exhibits a foot of the wave approximately 150 mV more positive than in the chloride electrolyte and the saturated photocurrent density is approximately 20% greater in the chloride electrolyte compared to the nitrate electrolyte. Also, the Faradaic efficiency (FE) for the OER is 87 ± 2% in the nitrate electrolyte compared to an FE of 100% for the oxidation of the chloride electrolyte to hypochlorous acid. These results suggest that the chloride ion rapidly injects electrons into the photogenerated holes in the H x WO 3 valence before these holes destructively recombine with W 5+ electron donors. The result is an increase in H x WO 3 stability during photoelectrochemical chloride oxidation when compared to water oxidation. FeOOH electrocatalysts are known to efficiently remove holes from photoresponsive metal oxides, and FeOOH was deposited on H x WO 3 . The H x WO 3 |FeOOH material also exhibits a negligible loss of photocurrent during OER and chloride oxidation, supporting this hypothesis.