Steering charge kinetics in photocatalysis: intersection of materials syntheses, characterization techniques and theoretical simulations

Abstract

Charge kinetics is highly critical in determining the quantum efficiency of solar-to-chemical conversion in photocatalysis, and this includes, but is not limited to, the separation of photoexcited electron-hole pairs, utilization of plasmonic hot carriers and delivery of photo-induced charges to reaction sites, as well as activation of reactants by energized charges. In this review, we highlight the recent progress on probing and steering charge kinetics toward designing highly efficient photocatalysts and elucidate the fundamentals behind the combinative use of controlled synthesis, characterization techniques (with a focus on spectroscopic characterizations) and theoretical simulations in photocatalysis studies. We first introduce the principles of various processes associated with charge kinetics that account for or may affect photocatalysis, from which a set of parameters that are critical to photocatalyst design can be summarized. We then outline the design rules for photocatalyst structures and their corresponding synthetic approaches. The implementation of characterization techniques and theoretical simulations in different steps of photocatalysis, together with the associated fundamentals and working mechanisms, are also presented. Finally, we discuss the challenges and opportunities for photocatalysis research at this unique intersection as well as the potential impact on other research fields.

Facet‐Engineered Surface and Interface Design of Photocatalytic Materials

“…The field promotes the electron‐hole separation along a particular direction and accumulates electrons and holes on the two side facets perpendicular to the field direction 11, 50, 51. This charge accumulation provides the opportunity for selecting facets to form interfaces through photo‐deposition.…”

“…The shift of CB and VB energy levels by surface states would directly alter the reduction and oxidation potentials of photogenerated carriers, respectively 11, 32. This feature has been recognized in the photocatalytic activity comparison between square‐shaped TiO 2 plate covered by {111} facet (T 111 , Figure 8i) and TiO 2 mainly enclosed with {001}, {101} or {010} facets (named as T 001 , T 101 or T 010 ) 17.…”

“…Firstly, polar facets may spontaneously induce a polarization effect 11, 50. In the CoO octahedrons enclosed with polar {111} plane ( Figure 9 a), internal electric field was established through the spontaneous polarization between the alternate layers of positive Co 2+ ions and negative O 2– ions along the [111] direction (Figure 9b) 62.…”

Probing the ultrafast dynamics in nanomaterial complex systems by femtosecond transient absorption spectroscopy

“…In this respect, time-resolved femtosecond pump-probe spectroscopy has become one of the most extensively adopted techniques since the advent of ultrafast laser systems that produce pulses with femtosecond duration in the early 1990s. Indeed, the importance as well as the robustness of time-resolved femtosecond pump-probe spectroscopy in unraveling the ultrafast dynamics in nanomaterials have been widely recognized, especially over the past decade [6][7][8][9][10] .…”

“…Email: qunzh@ustc.edu.cn, yiluo@ustc.edu.cn to obtain basic information on the structure, size, shape, and surface/interface of nanomaterials [4,5] . Nevertheless, in order to look into and better understand the structure-function interplay as well as the pertinent working mechanisms in nanomaterials, one has to step further to glean dynamic information about, e.g., the lifetime of charge carriers or excitons and their associated relaxation pathways [6][7][8][9][10] . These key, mechanistic insights into the dynamic evolution of nanomaterials can in turn offer valuable guidance to the rational design, synthesis, and implementation of nanomaterials [9] for many photochemical and photophysical applications, such as photocatalysis, photovoltaics, photoelectrochemistry and organic light-emitting diodes.…”