Cocatalysts For Water Splitting Research Articles

Plasmon-assisted spatially selective grafting of Ti3C2TX flakes for prevention of MXene oxidation and stability increase

The MXene flakes are considered excellent materials for a range of applications and device construction. Especially attractive is the utilization of MXenes as the catalysts or co-catalysts for water splitting, including both half-reactions – hydrogen (HER) and oxygen (OER) evolution. However, the MXenes exhibit a strong tendency to oxidize during utilization, especially in water media and at oxygen presence. The oxidation of the MXene flakes commonly starts from the edges and then proceeds to the basal planes. Since the catalytic activity of flakes is mostly related to the basal plane, strong covalent blocking of flake edges can significantly protect MXene in oxidative conditions and increase the flake’s lifetime without the loss of their catalytic activity. In this work, we demonstrated the combination of plasmon-assisted chemistry and electrochemistry for spatial-selective and precise modification of MXene (Ti3C2TX) flake edges. Our approach is based on the spatial distribution of plasmon energy under the flake’s illumination with infrared (IR) light. Plasmon local excitation leads to homolysis of the modification agent – iodonium salt, the formation of highly reactive radicals, and their immediate grafting to the edges of MXene flakes in the neighborhood. As a result, the edges of the flakes are protected, and the initial stage of their oxidation is prevented. After optimization of plasmon-assisted grafting, the modified flakes were tested in HER and OER and a significant increase in flakes stability was validated.

Photoelectrochemical performance of α-Fe2O3@NiOOH fabricated with facile photo-assisted electrodeposition method

This study adopted a photo-assisted electrodeposition method to fabricate NiOOH on α-Fe2O3 photoanode. The detailed microstructure and chemical composition characterizations suggested that the NiOOH particles were selectively deposited on the α-Fe2O3 surface to form hybrid nanocomposites. Photoelectrochemical measurements revealed the important role of NiOOH as a cocatalyst for water splitting under visible light illumination. The prepared photoanode exhibited essentially enhanced photoelectrochemical activity, which was about fourfold higher than that of α-Fe2O3 photoanode. Further study suggested that loading NiOOH by photo-assisted electrodeposition method on α-Fe2O3 surface can facilitate the water splitting process by providing substantial active reaction sites and promoting the transfer and consumption of photogenerated holes. Contribution of this work is to supply a facile method to develop efficient photoelectrochemical anode.

Metal-free graphene quantum dots photosensitizer coupled with nickel phosphide cocatalyst for enhanced photocatalytic hydrogen production in water under visible light

Photocatalytic hydrogen (H2) evolution is a promising approach for future sustainable energy utilization. However, it is still a great challenge to develop efficient and stable metal-free photocatalysts with broadband solar absorption in the visible region for H2 production. Metal-free graphene quantum dot (GQD) is an emerging candidate for this purpose because of its good water-solubility and tunable band gap. On the other hand, metal phosphides (Ni2P, Co2P, etc) have been demonstrated as novel noble-metal-free cocatalysts for water splitting, which can efficiently separate electron-hole pairs and enhance the photocatalytic activities. Herein, we report for the first time on the use of OH-functionalized GQDs (OH-GQDs) photosensitizer coupled with Ni2P nanoparticles for photocatalytic H2 production with λ > 420 nm light. The H2 production rate is ∼94 times higher than that of bare OH-GQDs, which is even comparable to that of OH-GQDs with 1.0 wt% Pt cocatalyst. This enhancement is probably due to the semiconductor-cocatalyst interface interaction between Ni2P and OH-GQDs to facilitate efficient charge transfer process.

Rationally designed/constructed MnOx/WO3 anode for photoelectrochemical water oxidation

Photoelectrocatalytic water splitting is an effective way to utilize the solar energy to solve the energy shortage. The valence band edge of WO3 located at ∼3V vs. normal hydrogen electrode (NHE), which can offer enough potential to kinetically oxidize water for oxygen evolution reaction. However, water oxidation reaction kinetics is sluggish when only WO3 is used as the photoanode. It is highly desirable to use cocatalyst to promote the kinetics. MnOx loaded on the WO3 photoanode through photodeposition methods improves the photoelectrochemical water oxidation performance. A maximum photocurrent density of composite photoanode is achieved with a deposition time of 3min, which is higher than that of pristine WO3 photoanode around 40%. MnO2 is not only a cocatalyst for water splitting but also for improving oxidation selectivity. We tried to use two means to load MnOx on WO3 photoanode material. It is observed that loading a moderate amount of MnOx on the WO3 by photodeposition can promote the performance of the WO3 photoanode.