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

Abstract

We develop a protocol for modeling photoelectrochemical reactions on semiconductor surfaces using density functional theory (DFT). We use an implicit solvation model of the electrolyte to implement an electronic grand canonical formalism for treating the variable charge state of the semiconductor surface under illumination and an applied bias. This protocol is applied to investigate the photodriven mechanism of the hydrogen evolution reaction (HER) over a cubic silicon carbide (3C-SiC) surface, which demonstrates that a Heyrovsky H2 generation step is rate-determining on the SiC (110) surface. The reaction free energy barrier of this step is heavily influenced by the surface charge density that is controlled by illumination and applied bias. The computed photon wavelengths required to overcome the Heyrovsky step barrier fall in the visible spectrum, thereby establishing the feasibility of HER reactions on the SiC (110) surface. Beyond offering insight into the HER mechanism on SiC, this work provides a general framework for modeling photo-electrochemical reactions occurring at an interface between a semiconductor surface and a liquid electrolyte.

Mechanistic Insight into the Photo-Oxidation of Perfluorocarboxylic Acid over Boron Nitride

“…Therefore, we further confirm the thermodynamic favorability of PFCA oxidation by computing the explicit reaction free energy for PFCA oxidation reaction on hBN (Figure a). Applying the same GC-DFT formalism from our previous work on a 4 × 4 hBN cell (the rightmost blue dotted line in Figure a), we find that the PFCA oxidation reaction to form a perfluoralkyl radical and CO 2 is favorable for positive surface charge densities higher than 12.5 μC cm –2 in the IS (this IS surface charge density corresponds to the presence of one hole on the 4 × 4 hBN surface). The oxidation reaction becomes more favorable when the surface charge density is increased as more holes are present on hBN.…”

“…We applied an electronic grand canonical density functional theory (GC-DFT) formalism, − which was developed in our previous work to study photoelectrochemical reactions on semiconductor surfaces, to calculate reaction energies and barriers as a function of variable surface charge under illumination. This approach allows one to model chemical reactions under constant illumination or applied potential, which is difficult in the usual canonical DFT formalism because the work function of the electrode surface changes significantly during the electron transfer reaction. , In this approach, we control the surface charge density by changing the total electron number in the system to match the desired potential of the semiconductor.…”

Electrocatalytic Site Activity Enhancement via Orbital Overlap in A2MnRuO7 (A = Dy3+, Ho3+, and Er3+) Pyrochlore Nanostructures

“…However, despite the limitations of our analysis, correlation between the bulk electronic structure from supercell DFT calculations and electrochemical responses enables identifying the nature of the key orbitals involved in the ORR and the OER. In order to formulate a more comprehensive mechanistic model, slab DFT calculations should be implemented (validated by surface structure analysis) incorporating water as a continuum 44 or explicitly, 45 which is a formidable challenge for such complex oxide structures.…”

Adsorption and Reductive Defluorination of Perfluorooctanoic Acid over Palladium Nanoparticles

“…On the Pd (111) surface, we calculated the adsorption energy of the PFOA molecule as where E Pd/PFOA is the energy of PFOA adsorbed on Pd (111), E Pd is the energy of the clean Pd (111) slab, and E PFOA is the energy of the isolated PFOA molecule. DFT calculations were performed with the Vienna Ab initio Simulation Package , (VASP 5.4.4) in conjunction with the VASPsol implicit solvation model. , Detailed calculation methods are provided in Supporting Information Section 2. − …”