Hydrogen peroxide (H₂O₂) photoproduction in seawater with metal-free photocatalysts derived from biomass materials is a green, sustainable, and ultra environmentally friendly way. However, most photocatalysts are always corroded or poisoned in seawater, resulting in a significantly reduced catalytic performance. Here, we report the metal-free photocatalysts (RUT-1 to RUT-5) with in-situ generated carbon dots (CDs) from biomass materials (Rutin) by a simple microwave-assisted pyrolysis method. Under visible light (λ ≥ 420 nm, 81.6 mW/cm²), the optimized catalyst of RUT-4 is stable and can achieve a high H₂O₂ yield of 330.36 μmol/L in seawater, 1.78 times higher than that in normal water. New transient potential scanning (TPS) tests are developed and operated to in-situ study the H₂O₂ photoproduction of RUT-4 under operation condition. RUT-4 has strong oxygen (O₂) absorption capacity, and the O₂ reduction rate in seawater is higher than that in water. Metal cations in seawater further promote the photo-charge separation and facilitate the photo-reduction reaction. For RUT-4, the conduction band level under operating conditions only satisfies the requirement of O₂ reduction but not for hydrogen (H₂) evolution. This work provides new insights for the in-situ study of photocatalyst under operation condition, and gives a green and sustainable path for the H₂O₂ photoproduction with metal-free catalysts in seawater.

Great attention has been paid to green procedures and technologies for the design of environmental catalytic systems. Biomass-derived catalysts represent one of the greener alternatives for green catalysis. Photocatalytic production of hydrogen peroxide (H₂O₂) from O₂ and H₂O is an ideal green way and has attracted widespread attention. Here, we show a metal-free photocatalyst from cellulose, which has a high photocatalytic activity for the photoproduction of H₂O₂ with the reaction rate up to 2,093 μmol/(h·g) and the apparent quantum efficiency of 2.33%. Importantly, a machine learning model was constructed to guide the synthesis of this metal-free photocatalyst. With the help of transient photovoltage (TPV) tests, we optimized their fabrication and catalytic activity, and clearly showed that the formation of carbon dots (CDs) facilitates the generation, separation, and transfer of photo-induced charges on the catalyst surface. This work provides a green way for the highly efficient metal-free photocatalyst design and study from biomass materials with the machine learning and TPV technology.

Highly efficient photo-assisted electrocatalysis for methanol oxidation reaction (MOR) realizes the conversion of solar and chemical energy into electric energy simultaneously. Here we report a Pt-MXene-TiO₂ composite for highly efficient MOR via a photoactive cascaded electro-catalytic process. With light (UV and visible light) irradiation, MXene-TiO₂ serves as the photo active centre (photoinduced hole) to activate the methanol molecules, while Pt particles are the active centre for the following electro-catalytic oxidation of those activated methanol molecules. Pt-MXene-TiO₂ catalyst exhibits a lower onset potential (0.33 V) and an impressive mass activity of 2,750.42 mA·mg^-1_Pt under light illumination. It represents the highest MOR activity ever reported for photo-assisted electrocatalysts. Pt-MXene-TiO₂ also shows excellent CO tolerance ability and stability, in which, after long-term (5,000 s) reaction, still keeps a high mass activity of 1,269.81 mA·mg^-1_Pt (62.66% of its initial activity). The photo-electro-catalytic system proposed in this work offers novel opportunities for exploiting photo-assisted enhancement of highly efficient and stable catalysts for MOR.

Hydrogen evolution by electrocatalysis is an attractive method of supplying clean energy. However, it is challenging to find cheap and efficient alternatives to rare and expensive platinum based catalysts. Pt provides the best hydrogen evolution performance, because it optimally balances the free energies of adsorption and desorption. Appropriate control of these quantities is essential for producing an efficient electrocatalyst. We demonstrate, based on first principles calculations, a stepwise designed Rh-Au-Si ternary catalyst, in which adsorption (the Volmer reaction) and desorption (the Heyrovsky reaction) take place on Rh and Si surfaces, respectively. The intermediate Au surface plays a vital role by promoting hydrogen diffusion from the Rh to the Si surface. Theoretical predictions have been explored extensively and verified by experimental observations. The optimized catalyst (Rh-Au-SiNW-2) has a composition of 2.2:28.5:69.3 (Rh: Au: Si mass ratio) and exhibits a Tafel slope of 24.0 mV·dec^–1. Its electrocatalytic activity surpasses that of a commercial 40 wt.% Pt/C catalyst at overpotentials above 0.19 V by exhibiting a current density of greater than 108 mA·cm^–2. At 0.3 V overpotential, the turnover frequency of Rh-Au-SiNW-2 is 10.8 times greater than that of 40 wt.% Pt/C. These properties may open new directions in the stepwise design of highly efficient catalysts for the hydrogen evolution reaction (HER).