Photoelectrochemical Generation of Green Hydrogen using Silicon Carbide

Supervisor: Dr Vishal Shah. Students must have a minimum Bachelors degree of 2.1 (UK) or international equivalent qualifications and a degree in experimental engineering/chemistry/physics.

In this proposal we intend on developing integrated semiconductor-electrocatalyst devices for the generation of green hydrogen using Silicon Carbide materials as the photoabsorber.

Silicon Carbide (SiC) is a wide bandgap semiconductor which has high critical electrical fields up to 2.8 MV/cm that result in advantages in power electronics as well as a high thermal conductivity (up to 4.5W/ (cm × K)) to allow high temperature operation. Moreover, it is extremely chemically stable. SiC has around 250 polymorphs. From this, only 4H-SiC (3.3 eV bandgap) has emerged as a commercial product on the market as the replacement to Silicon in power electronics. However, 4H-SiC requires its own dedicated substrate (up to 150 mm available), which are still expensive at ~£700 per wafer and which require a significant manufacturing thermal budget. 3C-SiC is a polytype with a slightly smaller bandgap (2.3 eV) and breakdown electric field (1.4 MV/cm), but can be grown on top of cheap Silicon substrates, up to 450mm in diameter. The development of 3C-SiC on Si is limited by defects, bow and thickness limitations due to the lattice mismatch between the Si and 3C-SiC.

3C-SiC has also shown promise in the photoelectrochemical (PEC) generation of H2, as the conduction and valence band positions of 3C-SiC ideally overlap the water redox potentials [1], allowing it to be used as both anode and cathode with photogenerated carriers and without external bias. The other advantages of 3C-SiC PEC are that it can be fabricated sustainably and at low costs, only requiring modest system complexity. It can moreover achieve an acceptable solar-to-hydrogen conversion efficiency > 10%, with current densities up to 8 mA/cm2[2]. The other main advantageous consideration is that since SiC is extremely chemically stable, hence has a chance of long-term, low maintenance implantation in the field.

For the use of only a standalone 3C-SiC layer, both PEC applications require thicknesses above 40 µm [1], which have previously required the use of expensive bulk growth. Hence, this proposal is timely due to the knowledge which has recently been developed at UoW for 3C-SiC epitaxy.

This studentship will expand on work being performed on a £100k grant won from the Henry Royce Institute. The successful student will both 1) develop 3C-SiC materials through nanostructuring the materials via conversion (e.g., SiC nanoparticles, SiC nanowires, SiC nanopores, trenching etc.) and 2) developing the overall SiC PEC system for hydrogen evolution and water-splitting through optimisation of a multi-material system with catalysts.

References:

[1] Jian et al. Sol. RRL 2020,4, 2000111

[2] Li et al. Catal. Sci. Technol., 2015, 5, 1360

Applications are open and rolling throughout the year, contact Dr Shah in the first instance (vishal.shah@warwick.ac.uk).