Efficient electrocatalyst of α-Fe2O3 nanorings for oxygen evolution reaction in acidic conditions

A novel 3D Fe2O3@ZnBi2O4 n-p heterojunction with high photocatalytic activity under visible light

A novel n-p Fe2O3@ZnBi2O4 (FZB) heterojunction with a unique 3D structure was fabricated in two simple steps to break down MB under visible light. First, the polymer gel combustion technique was employed to fabricate a 3D Fe2O3 framework. Next, a microwave-assisted precipitation approach was used to incorporate 3D ZnBi2O4 flakes onto the framework surface. FZB can effectively collect a broad range of UV-Vis light and sunlight. Surprisingly, the core-shell p-n heterojunction structure makes it easier for photogenerated charges to move and separate. This is because the semiconductor parts are better connected and the electric field is inside the two junctions. UV-Vis-DRS, EIS, PL, and XPS analyses confirmed this phenomenon. As a result, n-p FZB, with a Fe2O3/ZnBi2O4 molar ratio of 2 : 1, showed the highest photocatalytic activity, increasing the reaction rate by 4.2 times compared to Fe2O3 and 2.8 times compared to ZnBi2O4. Exposure to light for 100 min at a concentration of 0.7 g L-1 the FZB catalyst and pH = 9 led to the breakdown of more than 95% of the 50 ppm MB solution. In addition, the photodegradation of MB by n-p FZB increased the reaction rate by 2.15 times by adding hydrogen peroxide (H2O2), which is known as the photo-Fenton reaction. The efficacy showed remarkable photocatalytic activity, which increased the reaction rate by 5.95 times when persulfate was used. Finally, after examination of the energy band structure of the materials and the findings regarding the function of the oxidizing sites in the photocatalytic process, a reaction mechanism was proposed.

A novel electrochemical flow-cell for operando XAS investigations in X-ray opaque supports

Improvement of electrochemical technologies is one of the most popular topics in the field of renewable energy. However, this process requires a deep understanding of the electrode-electrolyte interface behavior under operando conditions. X-ray absorption spectroscopy (XAS) is widely employed to characterize electrode materials, providing element-selective oxidation state and local structure. Several existing cells allow studies as close as possible to realistic operating conditions, but most of them rely on the deposition of the electrodes on conductive and X-ray transparent materials, from where the radiation impinges the sample. In this work, we present a new electrochemical flow-cell for operando XAS that can be used with X-ray opaque substrates, since the signal is effectively detected from the electrode surface, as the radiation passes through a thin layer of electrolyte (∼17 μm). The electrolyte can flow over the electrode, reducing bubble formation and avoiding strong reactant concentration gradients. We show that high-quality data can be obtained under operando conditions, thanks to the high efficiency of the cell from the hard X-ray regime down to ∼4 keV. We report as a case study the operando XAS investigation at the Fe and Ni K-edges on Ni-doped γ-Fe2O3 films, epitaxially grown on Pt substrates. The effect of the Ni content on the catalytic performances for the oxygen evolution reaction is discussed.