Tuning Composition and Activity of Cobalt Titanium Oxide Catalysts for the Oxygen Evolution Reaction

Probing Changes in the Local Structure of Active Bimetallic Mn/Ru Oxides during Oxygen Evolution

Identifying the active site of catalysts for the oxygen evolution reaction (OER) is critical for the design of electrode materials that will outperform the current, expensive state-of-the-art catalyst, RuO2. Previous work shows that mixed Mn/Ru oxides show comparable performances in the OER, while reducing reliance on this expensive and scarce Pt-group metal. Herein, X-ray photoelectron spectroscopy and X-ray absorption spectroscopy (XAS) are performed on mixed Mn/Ru oxide materials for the OER to understand structural and chemical changes at both metal sites during oxygen evolution. The results show that the Mn-content affects both the oxidation state and local coordination environment of Ru sites. Operando XAS experiments suggest that the presence of MnOx might be essential to achieve high activity likely by facilitating changes in the O-coordination sphere of Ru centers.

Synergistic effect of p-type and n-type dopants in semiconductors for efficient electrocatalytic water splitting

The main challenge for acidic water electrolysis is the lack of active and stable oxygen evolution catalysts based on abundant materials, which are globally scalable. Iridium oxide is the only material which is active and stable. However, Ir is extremely rare. While both active materials and stable materials exist, those that are active are usually not stable and vice versa. In this work, we present a new design strategy for activating stable materials originally deemed unsuitable due to a semiconducting nature and wide band gap energy. These stable semiconductors cannot change oxidation state under the relevant reaction conditions. Based on DFT calculations, we find that adding an n-type dopant facilitates oxygen binding on semiconductor surfaces. The binding is, however, strong and prevents further binding or desorption of oxygen. By combining both n-type and p-type dopants, the reactivity can be tuned so that oxygen can be adsorbed and desorbed under reaction conditions. The tuning results from the electrostatic interactions between the dopants as well as between the dopants and the binding site. This concept is experimentally verified on TiO₂ by co-substituting with different pairs of n- and p-type dopants. Our findings suggest that the co-substitution approach can be used to activate stable materials, with no intrinsic oxygen evolution activity, to design new catalysts for acid water electrolysis.

Highly Active Oxygen Evolution on Carbon Fiber Paper Coated with Atomic-Layer-Deposited Cobalt Oxide

In this work, we evaluated the oxygen evolution performance of cobalt oxide (CoO _x)-coated carbon fiber paper in electrochemical water splitting. For a uniform coating of CoO _x layers along the carbon fiber paper, the atomic layer deposition (ALD) technique was applied. We achieved a uniform and conformal coating of atomic-layer-deposited CoO _x (ALD-CoO _x) on the carbon fiber paper. The overpotential for oxygen evolution measured for the optimized ALD-coated carbon fiber paper was as low as 343 mV at 10 mA cm^-2, which is competitive with the activity of state-of-the-art CoO _x prepared on electrodes with large surface areas. Oxygen evolution is not enhanced after a critical thickness, about 28 nm in our study, is reached. The optimal thickness of the ALD-CoO _x film is dependent on two competing effects: the high oxidation state of cobalt ions in thicker CoO _x helps the oxygen evolution, whereas the introduction of a thick oxide coating decelerates the rate of charge transfer at the surface.

Phosphorization engineering ameliorated the electrocatalytic activity for overall water splitting on Ni3S2 nanosheets

Ni₃S₂–Ni₂P heterostructure nanosheets serve as a highly efficient water-splitting electrocatalyst in an alkaline medium.

Engineering NiS/Ni2P Heterostructures for Efficient Electrocatalytic Water Splitting

Developing high-active and low-cost bifunctional materials for catalyzing the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) holds a pivotal role in water splitting. Therefore, we present a new strategy to form NiS/Ni₂P heterostructures. The as-obtained NiS/Ni₂P/carbon cloth (CC) requires overpotentials of 111 mV for the HER and 265 mV for the OER to reach a current density of 20 mA cm^-2, outperforming their counterparts such as NiS and Ni₂P under the same conditions. Additionally, the NiS/Ni₂P/CC electrode requires a 1.67 V cell voltage to deliver 10 mA cm^-2 in a two-electrode electrolysis system, which is comparable to the cell using the benchmark Pt/C||RuO₂ electrode. Detailed characterizations reveal that strong electronic interactions between NiS and Ni₂P, abundant active sites, and smaller charge-transfer resistance contribute to the improved HER and OER activity.