Epitaxial Cubic Silicon Carbide Photocathodes for Visible‐Light‐Driven Water Splitting

Abstract

Cubic silicon carbide (3C‐SiC) material feature a suitable bandgap and high resistance to photocorrosion. Thus, it has been emerged as a promising semiconductor for hydrogen evolution. Here, the relationship between the photoelectrochemical properties and the microstructures of different SiC materials is demonstrated. For visible‐light‐derived water splitting to hydrogen production, nanocrystalline, microcrystalline and epitaxial (001) 3C‐SiC films are applied as the photocathodes. The epitaxial 3C‐SiC film presents the highest photoelectrochemical activity for hydrogen evolution, because of its perfect (001) orientation, high phase purity, low resistance, and negative conduction band energy level. This finding offers a strategy to design SiC‐based photocathodes with superior photoelectrochemical performances.

Density Functional Theory Modeling of Photo-electrochemical Reactions on Semiconductors: H2 Evolution on 3C-SiC

“…Yasuda et al doped several polytypes (3C-, 4H-, 6H-) of SiC with p-type impurities and showed that photodriven HER could be achieved with solar irradiation on all SiC polytypes even in the absence of an applied bias. These early successes motivated other studies in several directions, such as doping SiC with p/n-type impurities, , using cocatalysts, modifying the surface via acid oxidation, using heterostructure composites, − and engineering various SiC nanostructures. − …”

Revisiting the Strongly Correlated Si-Terminated 3C-SiC(001)-p(2 × 1) Reconstructed Surface with Single- and Multiconfigurational Methods

“…The two outer Si dimer atoms are saturated with an additional H atom to prevent the cluster from having two dimer atoms not interacting with neighboring dimers, providing reasonable embedding of the surface states in between. This saturation also reduces the size of the active space from a maximum of CAS (12,12) to CAS(10,10) for this particular example, overall enabling the construction of slightly larger cluster models. From an electronic structure perspective, it is probably more reasonable to classify this 3 × 1-dimer cluster model as a twodimer cluster since it only consists of one real dimer with the full CAS (4,4), two half-dimers with a CAS(2,2) ("half σ bond" + dangling bond) each, and the capping H-saturated halfdimers with a CAS(1,1) ("half σ bond") each.…”

“…Furthermore, the band gap of 3C-SiC straddles the redox potentials of the hydrogen and oxygen evolution reactions, making it a promising candidate for photoelectrochemical water splitting . However, preparing high-quality single-crystal 3C-SiC samples remains challenging as they are only accessible by vapor deposition techniques on Si or hexagonal SiC substrates, which is why only little experimental work has been conducted regarding photoelectrochemical water splitting on this material. ,− A large fraction of the 3C-SiC thin films are grown on Si(001) substrates, resulting in 3C-SiC(001) being the most common surface, − which in the stoichiometric case is either terminated by a monolayer of Si or C. Theoretical studies indicate the Si- and C-terminated surfaces to be hydrophilic and hydrophobic, respectively, − making the former potentially more suitable for water-splitting applications.…”

Nanostructured 3C-SiC on Si by a network of (111) platelets: a fully textured film generated by intrinsic growth anisotropy

“…, heat sink layers for power devices (SiC is an excellent heat conductor, just below diamond) and photocathodes for electrochemical water splitting systems, since 3C-SiC displays the best band structure that straddles the water redox potentials. 11,12…”

“…Such a morphology could be interesting for novel 3C-SiC applications, i.e., heat sink layers for power devices (SiC is an excellent heat conductor, just below diamond) and photocathodes for electrochemical water splitting systems, since 3C-SiC displays the best band structure that straddles the water redox potentials. 11,12 Actually, the large anisotropy in the three-dimensional (3D) growth velocity of different facets of 3C-SiC microcrystals on Si micropillars has already been demonstrated, 13 indicating a very slow growth of {111} facets, progressively extending in size. Indeed, the kinetic origin of such behaviour is suggested by the fact that polycrystalline films deposited by CVD at 1250 1C, with silicon-tetrachloride and toluene precursors, result in highly (111)-oriented crystallites of pyramidal shape with hexagonal basis (by twinning), whereas using methane in place of toluene gives rise to randomly oriented coatings with cauliflower-like crystallites.…”