Electrocatalytic water splitting is a promising approach to harness the power of hydrogen, a clean fuel that can be burnt in air to release energy and produce only water as the byproduct. Most catalysts for the hydrogen and oxygen evolution reactions, such as precious metals, are expensive, scarce, and difficult to source. Cheaper, Earth-abundant alternatives do exist, but they are plagued by high overpotentials and low efficiencies.
An active area of research involves the design of modification schemes for these alternatives to improve their performance as electrocatalysts. Parija et al. investigated selenium substitution on the anion sublattice and interfacial hybridization with molybdenum trioxide (MoO3) to enhance the catalytic activity of molybdenum disulfide (MoS2). The resulting MoS2-xSex/MoO3 heterostructures demonstrate several improvements, including low overpotentials, high current densities, high turnover frequencies, and prolonged operation.
This modification scheme came about as a result of closed loop X-ray absorption and emission spectroscopy measurements of electronic structure, as well as density functional theory calculations. The researchers realized replacing some sulfide with selenium would enhance activity towards oxygen evolution, while the interfacial hybridization with MoO3 would do the same for hydrogen evolution.
The MoS2-xSex/MoO3 heterostructures were prepared with a sol-gel process, followed by thermal annealing and hydrothermal synthesis, and finally integrated onto carbon fiber paper. They showed excellent electrocatalytic activity for hydrogen and oxygen evolution reactions.
The work highlights the potential of modulating crystal and electronic band structure to enhance the performance of inexpensive, Earth-abundant alternatives for electrocatalytic water splitting. As a further step, the collaborative team is exploring photocatalytic water splitting by adding a light absorber to the system to create an “artificial leaf” that would also remove carbon dioxide from the air.
Source: “Electronic structure modulation of MoS2 by substitutional Se incorporation and interfacial MoO3 hybridization: Implications of Fermi engineering for electrocatalytic hydrogen evolution and oxygen evolution,” by Abhishek Parija, Wasif Zaheer, Junsang Cho, Theodore E. G. Alivio, Sirine C. Fakra, Mohammed Al-Hashimi, David Prendergast, and Sarbajit Banerjee, Chemical Physics Reviews (2021). The article can be accessed at http://doi.org/10.1063/5.0037749.
