Pongkarn Chakthranont

Materials for solar fuels and chemicals

The conversion of sunlight into fuels and chemicals is an attractive prospect for the storage of renewable energy, and photoelectrocatalytic technologies represent a pathway by which solar fuels might be realized. However, there are numerous scientific challenges in developing these technologies. These include finding suitable materials for the absorption of incident photons, developing more efficient catalysts for both water splitting and the production of fuels, and understanding how interfaces between catalysts, photoabsorbers and electrolytes can be designed to minimize losses and resist degradation. In this Review, we highlight recent milestones in these areas and some key scientific challenges remaining between the current state of the art and a technology that can effectively convert sunlight into fuels and chemicals.

Development of a reactor with carbon catalysts for modular-scale, low-cost electrochemical generation of H2O2

The development of small-scale, decentralized reactors for H2O2 production that can couple to renewable energy sources would be of great benefit, particularly for water purification in the developing world. Herein, we describe our efforts to develop electrochemical reactors for H2O2 generation with high Faradaic efficiencies of >90%, requiring cell voltages of only ∼1.6 V. The reactor employs a carbon-based catalyst that demonstrates excellent performance for H2O2 production under alkaline conditions, as demonstrated by fundamental studies involving rotating-ring disk electrode methods. The low-cost, membrane-free reactor design represents a step towards a continuous, modular-scale, de-centralized production of H2O2.

Understanding activity trends in electrochemical water oxidation to form hydrogen peroxide

Electrochemical production of hydrogen peroxide (H2O2) from water oxidation could provide a very attractive route to locally produce a chemically valuable product from an abundant resource. Herein using density functional theory calculations, we predict trends in activity for water oxidation towards H2O2 evolution on four different metal oxides, i.e., WO3, SnO2, TiO2 and BiVO4. The density functional theory predicted trend for H2O2 evolution is further confirmed by our experimental measurements. Moreover, we identify that BiVO4 has the best H2O2 generation amount of those oxides and can achieve a Faraday efficiency of about 98% for H2O2 production.Producing hydrogen peroxide via electrochemical oxidation of water is an attractive route to this valuable product. Here the authors theoretically and experimentally investigate hydrogen peroxide production activity trends for a range of metal oxides and identify the optimal bias ranges for high Faraday efficiencies.

Mapping Photoelectrochemical Current Distribution at Nanoscale Dimensions on Morphologically Controlled BiVO4.

We develop a method that can be used to qualitatively map photocurrent on photoelectrode surfaces, and show its utility for morphologically controlled W-doped BiVO4. The method is based on the deliberate photoinduced sintering of Au NPs, a photon-driven process that indicates oxidation with nanoscale-resolution. This strategy allows us to identify the active regions on W-doped BiVO4 photoelectrodes, and we observe a strong dependence of photoactivity on the electrode morphology, controlled by varying the relative humidity during the sol-gel fabrication process. We find that photoelectrode morphologies that exhibit the most evenly distributed Au sintering are those that yield the highest photoelectrochemical (PEC) activity. Understanding the correlation between electrode morphology and PEC activity is essential for designing structured semiconductors for PEC water splitting.

Top-down fabrication of fluorine-doped tin oxide nanopillar substrates for solar water splitting

Because of its high electronic conductivity, electrochemical stability, and optical transparency, fluorine-doped tin oxide (FTO) is a frequently used substrate for photoelectrochemical water splitting (PEC), dye-sensitized solar cells (DSSCs) and other electrocatalytic systems. These applications often require high surface-area substrates, but typical wet-chemical and lithographic approaches to nanostructure this promising material have been limited by the toxic fluorine ion and the resistance of tin oxide to standard chemical etchants. In this work, we develop a novel process to nanostructure commercial FTO by combining nanosphere lithography with argon ion-milling. We show nanostructured FTO with nanopillars of tunable height and diameter. Depositing tungsten oxide with atomic layer deposition on the nanostructured FTO substrate yields a PEC photoanode improvement of 40% over the baseline FTO substrate. The improvement is ascribed mainly to the increased roughness factor achieved by nanostructuring the substrate.