Designing High-Efficiency Photocatalysts—Insights from a Photo-Assisted Kelvin Probe Force Microscopy Study

Introducing dopants and constructing heterostructures are viable strategies for separating electron-hole pairs by creating energy barriers, such as the Schottky barrier or built-in potential, at the interfaces between two photocatalysts. In the case of a heterostructure photocatalyst, the surface potential difference between the parent material and the co-catalyst plays a decisive role in determining the photocatalyst's photoreduction or photooxidation abilities. Consequently, understanding and manipulating this surface potential difference is instrumental in designing the nanostructure of photocatalysts.<br/>Kelvin Probe Force Microscopy (KPFM) is a direct and straightforward technique for measuring the surface potential of a material. By utilizing KPFM with various light sources ranging from UV to red light, the surface potential of materials can be characterized either under light illumination or in the absence of light. The surface potential, referred to as the contact potential difference (CPD) of a material, can be quantified using <b>Equation (1)</b>.<br/><br/>CPD=(Φ_tip-Φ_sample)/e <b>Equation (1)</b><br/>ΔCPD=CPD_{under light illumination}-CPD_{under dark condition}<b>Equation (2)</b><br/><br/>Here, Indicates the material’s potential difference under light illumination and dark conditions. Therefore, can be obtained from the <b>Equation 2</b>. The increased for a material after light illumination indicates a high electron density present at the material's surface. The is closely linked to the light response and electron generation in the material. Therefore, a larger indicates a higher activity of photocatalysts because it leads to the excitation of more charges.<br/>Observing the surface potential evolution of different materials allows for a rational prediction of how to pattern a material that can achieve the highest photocatalytic activity. This technique provides a promising path for designing novel materials. In this work, I will detail our research group's strategic approach to enhancing photocatalytic activities for different applications: (1) photoreduction, (2) photocatalytic hydrogen production, (3) plastic photoreforming, and (4) CO₂ reduction. Our findings offer a deeper understanding of carrier transport routes in heterostructures and provide valuable insights for designing future photocatalytic materials.