2. In Situ Irradiated X-ray Photoelectron Spectroscopy Investigation
on
Electron Transfer Mechanism in S-Scheme Photocatalyst
ABSTRACT: S-scheme photocatalysts have demonstrated great potential in solar fuel production. To study the
electron transfer pathways in S-scheme heterojunctions, in situ irradiated X-ray photoelectron spectroscopy
(ISIXPS) is an effective and widely used technology. However, the mechanism of ISIXPS in identifying the
electron transfer pathways in S-scheme heterojunction has not yet been elucidated. In this Perspective, the
development process and the formation mechanism of S-scheme photocatalysts are first introduced.
Afterward, the principles of XPS and ISIXPS measurements are thoroughly explained, and the applications of
XPS and ISIXPS in confirming the interfacial electron transfer in Sscheme heterojunctions are discussed. Finally,
suggestions for future research on the utilization of ISIXPS in S-scheme heterojunctions are proposed. This
Perspective will provide deep insight into the electron transfer mechanism in S-scheme photocatalysts through
ISIXPS.
Key Words :Z-scheme systems, semiconductor photocatalysts, ISIXPS, measurements
3. Introduction : Because of significant economic and social growth, energy consumption is increasing. The overuse and use of fossil
fuels has resulted in an energy crisis.Pollution of the environment 1−4 The transition from fossil fuels to renewable energy is critical
to achieving carbon neutrality. Solar energy is a renewable energy source that is both clean and abundant. 5−7One of the most
promising solar energy use technologies is emerging semiconductor photocatalysis. At room temperature and pressure,
photocatalytic water splitting and photocatalytic CO2 reduction may transform solar energy into storable and transportable
chemical fuels (also known as solar fuels, such as hydrogen and methanol). 8−10The fast recombination of photogenerated
electrons and holes is now the most important scientific topic in photocatalysis.11−13 Because photogenerated carriers are easily
recombined inside photocatalysts for single semiconductor photocatalysts,
Because of significant economic and social growth, energy consumption is increasing. The overuse and use of fossil fuels has resulted
in an energy crisis.Pollution of the environment1−4 The transition from fossil fuels to renewable energy is critical to achieving carbon
neutrality. Solar energy is a renewable energy source that is both clean and abundant. 5−7One of the most promising solar energy use
technologies is emerging semiconductor photocatalysis. At room temperature and pressure, photocatalytic water splitting and
photocatalytic CO2 reduction may transform solar energy into storable and transportable chemical fuels (also known as solar fuels,
such as hydrogen and methanol). 8−10The fast recombination of photogenerated electrons and holes is now the most important
scientific topic in photocatalysis.11−13 Because photogenerated carriers are easily recombined inside photocatalysts for single
semiconductor photocatalysts,
4. In terms of dynamics, the repulsion between electrons (or holes) in SI and electrons (or holes)
in SII, as well as the electronhole attraction, impede charge transfer between SI and SII.as well
as SII In 1979, Bard suggested conventional (liquid) Z-scheme systems with appropriate redox
ion pairs (RIPs) to boost the redox capacity of photocatalytic systems, inspired by natural
photosynthesis of plants. 16 RIPs are typically made of of an electron acceptor and an electron
donor (for example, Fe3+/Fe2+). The claimed electron transport mechanism in classic Z-
scheme devices is discovered to be inaccurate after serious investigation (Figure 1b).
Thermodynamically and electrochemically, Fe3+ is more likely to take electrons from the CB of
SII, whereas Fe2+ is more quickly oxidised by the holes in SI. Furthermore, the presence of RIPs
limits the use of typical Z-scheme systems to the liquid phase. Tada et al. developed an all-
solid-state Z-scheme heterojunction in 2006 to overcome this limitation. 17 Solid metal
conductors are employed to replace the RIPs, allowing Z-scheme photocatalysts to be utilised
in gas/solid-phase processes. However, the electron transport mechanism in all-solid-state Z-
scheme heterojunctions suffers from the same issue as in classic Z-scheme systems.
