Accurate exploration of synergistic thermal effect: Low-grade-heat-promoted charge recombination coupled with spherical incidence for efficient sunlight-driven photocatalysis

Abstract

The major objective of the emerging photo-thermo-catalysis is using waste heat to boost the photocatalytic reaction, especially that powered by sunlight. Because of the complex composition of light-intensity-dependent apparent activation energies, the issue that principally hinders the synergistic thermal effect to photocatalysis has hardly been accurately explored. In this work, by virtue of mutual match of theoretical simulation and experimental behaviors, we demonstrate that photocatalytic reaction rates exhibit a sensitively positive correlation with temperature under weak illumination, in which charge recombination predominates the rate-determining step of semiconductor–cocatalyst interfacial electron transfer. Under high-intensity irradiation, however, the aggravation of charge leakage inherently accompanied by thermionic emission severely weakens the synergistic thermal effect or even slows down the reaction by raising the temperature. Inspired by these, we manage to maximize the photocatalytic solar utilization by spherical incidence of sunlight with the assistance of low-grade heat.

Revealing and Facilitating the Rate-Determining Step for Efficient Sunlight-Driven Photocatalysis

“…As expected, the time constants for SM interfacial electron transfer estimated from the OCP behaviors become smaller with an increase in temperature (Figure and Figure S6). Like the situation triggered by light (Figure ), the τ iet estimated from the OCP after removing potential bias also increases evidently as the potential becomes less negative, especially for the case of CdS (Figure ). These behaviors imply that the advantages of Al-CdS over CdS become evident as the light becomes weak.…”

“…With an increase in temperature, Al-CdS takes growing advantage of the synergistic thermal effect over CdS by promoting charge recombination (Figure S10). When the illumination is weaker (50 mW/cm 2 ), the increase in the contribution by charge recombination makes the synergistic thermal effect evident for the cases of CdS. This makes HE rate plots for Pt/Al-CdS and Pt/CdS parallel each other with a multiple of ∼5.75 (Figure b).…”

“…The thermal effect has recently been incorporated into photocatalytic reaction to address the issue described above by heat–light synergy. − However, because the composition of the apparent activation energy is complex, an increase in temperature does not unconditionally facilitate the photocatalytic reaction. − To take full advantage of the synergistic thermal effect, it is important to explore the rate-determining step and maximize its positive correlation with temperature.…”

“…The rate ( r iet ) of SM interfacial electron transfer can be given by because SM interfacial electron transfer is the rate-determining step, the photocatalytic utilization ( U ), which, unfortunately, exhibits a minimal value near the intensity of sunlight for some common systems (Figure S2), can be approximately given by where k te and k cr are the pseudo-rate constants for thermionic emission and charge recombination, respectively, after separation of the variable of incident photons ( P inc ). Thermionic emission, which numerically and also physically is the major approach for SM interfacial electron transfer under intense irradiation, displays inert or even negative correlation with temperature . In contrast, charge recombination, which dominates the SM interfacial electronic process under weak illumination, exhibits an evident positive correlation with temperature .…”

“…Thermionic emission, which numerically and also physically is the major approach for SM interfacial electron transfer under intense irradiation, displays inert or even negative correlation with temperature . In contrast, charge recombination, which dominates the SM interfacial electronic process under weak illumination, exhibits an evident positive correlation with temperature . In addition, because the occurrence of charge recombination relies on the intermediate sites, , it is rational to increase the density of surface states to facilitate SM interfacial electron transfer (Figures and and Figure S3).…”