Imaging photogenerated charge carriers on surfaces and interfaces of photocatalysts with surface photovoltage microscopy

Abstract

Understanding photogenerated charge separation on the nano- to micrometer scale is the key to optimizing the photocatalytic solar energy conversion efficiency. In the past few years, spatially resolved surface photovoltage (SPV) techniques have opened up new opportunities to directly image localized charge separation at surfaces or interfaces of photocatalysts and thus provided deep insights into the understanding of photocatalysis. In this review, we reviewed the SPV techniques, in particular Kelvin probe force microscopy (KPFM) based spatially resolved SPV techniques and their applications in charge separation imaging. The SPV principle was explained with regard to charge separation across a space charge region (SCR) in a depletion layer at a semiconductor surface and to diffusion. The center of charge approach, relaxation of SPV signals and measurement of SPV signals including SPV transients with fixed capacitors were described. Then, we highlighted the fundamental principle and development of the spatially resolved SPV technique and its application in photocatalysis. Important progress made by the spatially resolved SPV technique in this group is given, focusing on understanding the nature of charge separation and providing insights into the rational design of highly efficient photocatalytic systems. Finally, we discuss the prospects of further developments of the spatially resolved SPV technique that would help in understanding photocatalysis for solar energy conversion with high temporal resolution and operated under in operando conditions.

Surface‐Polarity‐Induced Spatial Charge Separation Boosts Photocatalytic Overall Water Splitting on GaN Nanorod Arrays

“…As ΔCPD reflects the extent of surface band bending, accordingly, the upward band bending of the polar surface is more obvious than the nonpolar surface, as depicted in Figure g. In this case, the photogenerated electrons are more likely to be transferred to the nonpolar surface, while the photogenerated holes flow to the polar surface under illumination. As a result, the difference in surface band bending leads to the spatial separation of photogenerated electrons and holes between the polar and nonpolar surfaces.…”

A Hybrid Artificial Photocatalysis System Splits Atmospheric Water for Simultaneous Dehumidification and Power Generation

“…Systems based on ferroelectric–semiconductor, typically requiring an external energy for polarization pretreatment, also suffers from a limitation of degeneration with the polarized built‐in electric field over time . “Crystal plane engineering” is an efficient method for exposing different crystal planes in a nanoparticle, which aids in achieving difference surface potentials at various planes ascribed to the varied atomic arrangements . Using this strategy, a polarizing electric field can be induced between crystal planes.…”

“…[11][12][13] "Crystal plane engineering" is an efficient method for exposing different crystal planes in a nanoparticle, which aids in achieving difference surface potentials at various planes ascribed to the varied atomic arrangements. [6,[14][15][16] Using this strategy, a polarizing electric field can be induced between crystal planes. Hence, by exploiting crystal planes' electric filed to orient ferroelectric dipole in a nanoparticle, it is possible to drive photocatalyst water splitting without extra energy for polarization and enhance the photogenerated charge's mobility.…”

Surface‐Polarity‐Induced Spatial Charge Separation Boosts Photocatalytic Overall Water Splitting on GaN Nanorod Arrays

“…As DCPD reflects the extent of surface band bending, [24] accordingly,the upward band bending of the polar surface is more obvious than the nonpolar surface,a sd epicted in Figure 3g.Inthis case,the photogenerated electrons are more likely to be transferred to the nonpolar surface,w hile the photogenerated holes flow to the polar surface under illumination. As ar esult, the difference in surface band bending leads to the spatial separation of photogenerated electrons and holes between the polar and nonpolar surfaces.…”