Atomic force microscopy: Emerging illuminated and operando techniques for solar fuel research

Abstract

Integrated photoelectrochemical devices rely on the synergy between components to efficiently generate sustainable fuels from sunlight. The micro-and/or nanoscale characteristics of the components and their interfaces often control critical processes of the device, such as charge-carrier generation, electron and ion transport, surface potentials, and electrocatalysis. Understanding the spatial properties and structure-property relationships of these components can provide insight into designing scalable and efficient solar fuel components and systems. These processes can be probed ex situ or in situ with nanometer-scale spatial resolution using emerging scanning-probe techniques based on atomic force microscopy (AFM). In this Perspective, we summarize recent developments of AFM-based techniques relevant to solar fuel research. We review recent progress in AFM for (1) steady-state and dynamic light-induced surface photovoltage measurements;(2) nanoelectrical conductive measurements to resolve charge-carrier heterogeneity and junction energetics; (3) operando investigations of morphological changes, as well as surface electrochemical potentials, currents, and photovoltages in liquids. Opportunities for research include: (1) control of ambient conditions for performing AFM measurements; (2) in situ visualization of corrosion and morphological evolution of electrodes; (3) operando AFM techniques to allow nanoscale mapping of local catalytic activities and photo-induced currents and potentials.

Electrospun TiO2‐Based Photocatalysts

“…Solar energy is an inexhaustible, pollution‐free, and environment‐friendly renewable energy source, on which scientists have set great hopes for replacing the depleting fossil energy. [ 13–17 ]…”

In Situ Analytical Techniques for the Investigation of Material Stability and Interface Dynamics in Electrocatalytic and Photoelectrochemical Applications

“…[169][170][171][172][173][174] However, biasing an insulated conductive probe with only the tip exposed as a second independent working electrode in a four-electrode system enables SECM via the AFM tip. [175] This four-electrode EC-AFM can map the local electrochemical activity or potential at the electrode surface along with the topography at sub-100 nm resolution. [175][176][177][178] EC-AFM has allowed researchers to monitor the potentialdependence of in situ changes to electrocatalyst surface roughness at the nanoscale.…”

“…[175] This four-electrode EC-AFM can map the local electrochemical activity or potential at the electrode surface along with the topography at sub-100 nm resolution. [175][176][177][178] EC-AFM has allowed researchers to monitor the potentialdependence of in situ changes to electrocatalyst surface roughness at the nanoscale. Dette et al, for example, used EC-AFM to study how the addition of Co to nanosheets of the OER catalyst NiO x H y changed the porosity of the structure and enhanced its stability during electrochemical cycling.…”

TiO 2 , ZnO, and SnO 2 -based metal oxides for photocatalytic applications: principles and development

“…The photogenerated charge carriers' relaxation time can be studied using time resolved fluorescence spectroscopy, transient absorption spectroscopy [25,26], or time resolved microwave conductivity [27]. Spatial distribution can be determined by Kelvin probe force microscopy (KPFM) [28], electrostatic force microscopy (EFM) [29], or conductive atomic force microscopy (C-AFM) [30].…”