Robert Holt

Photocatalytic water splitting has attracted significant attention as a low-cost, clean, and green method for the conversion of solar energy into hydrogen, highlighting its potential to solve energy and environmental problems. In this work, we report the coupling of a plasmonic resonator with semiconductor quantum dots (QDs) for enhancement in photoelectrocatalytic water splitting toward hydrogen (H2) production. Specifically, cadmium selenide (CdSe) QDs were deposited on silver nano-gratings (Ag gratings). Plasmonic enhancement was observed in the absorption/emission of QDs using our angle-resolved steady-state optical spectroscopy. Furthermore, angle-resolved absorption spectra helped us to optimize the illumination conditions for resonant excitation using a setup for photoelectrochemical (PEC) experiments. Under the resonant pump, the emission of the QDs has been plasmonically enhanced with a Purcell factor (FP) of ∼1.5. Our numerical simulation revealed a strong near-field enhancement due to the excitation of surface plasmon resonances, contributing to FP. A similar enhancement order in the PEC experiments was also observed under resonant pump conditions, indicating the contribution of plasmon resonances to the enhanced photoelectrocatalysis. Switching the excitation's polarization further reinforces this, resulting in an enhanced photocurrent under p-polarization. These findings provide a proof of concept, thus laying the foundation for a practical device for efficient solar-to-H2 conversion.

The dehydration and high temperature carbonation reactions of Ca(OH)₂ are an essential part of a number of existing schemes aiming to apply the thermochemical CaO–CaCO₃ cycle (‘Ca Looping’) in emerging energy industries such as CO₂ capture, gasification and thermal energy storage. However, the underlying chemical mechanisms are poorly understood and the reaction kinetics exhibit a number of strange features such as the increased thermal stability of Ca(OH)₂, dubbed “superheating”, observed in the presence of CO₂. In this work, in situ X-ray diffraction (XRD) measurements using a synchrotron source are coupled with full pattern fitting analysis to provide high-resolution and high-accuracy data on the evolution of Ca(OH)₂ crystalline structural parameters during the dehydration and carbonation reactions. This method has allowed new observations to be made that provide insight into the studied reaction mechanisms and disprove existing hypotheses as to the origin of superheating. A new hypothesis, involving the formation of an intermediate and permeable Ca(OH)₂ structure was formulated which can explain the growing body of observations in this area.