Photoelectrochemical Properties of CH₃-Terminated p-Type GaP(111)A

Abstract

The photoelectrochemical properties of p-type gallium phosphide (GaP) (111)A electrodes before and after a two-step chlorination/Grignard reaction sequence have been assessed. Electrochemical impedance spectroscopy indicated both a change in the flat-band potential in water and decreased sensitivity of the band edge energetics toward pH for GaP(111)A surfaces following modification. Separate stability tests were performed to gauge the susceptibilities of unmodified and CH 3 -terminated p-GaP(111)A photoelectrodes toward reductive degradation under illumination. The steady-state photoelectrochemical results showed modification of GaP(111)A with −CH 3 groups significantly enhanced p-GaP stability. Separately, sub-bandgap photocurrent measurements were collected to assess relative changes in surface states acting as recombination centers. In the absence of any dye, the sub-bandgap photocurrent from trapping/detrapping of charge carriers in surface states was higher for unmodified p-GaP photoelectrodes than for CH 3 -terminated p-GaP(111)A. Further, sensitized photocurrents of p-GaP photoelectrodes with Brilliant Green were systematically higher after modification with −CH 3 groups, indicating a deactivation of a surface recombination pathway after surface modification. Collectively, this work illustrates a rational chemical strategy to modify and augment the pertinent interfacial properties of p-GaP photocathodes in an aqueous photoelectrochemical system.

Computational Approaches to Photoelectrode Design through Molecular Functionalization for Enhanced Photoelectrochemical Water Splitting

“…Organic molecule functional groups have been shown to effectively enhance photoelectrode stability against photocorrosion (referred to as photoelectrode stability henceforth), typically through chemical passivation of surface dangling bonds . Refs.…”

“…Extending the computational modeling of photocorrosion reaction pathways discussed in Section 2.2 to functionalized photoelectrodes will be crucial to design stable functional groups. For surfaces that are widely studied in experiments such as Si(111) and GaP(111), there already exists a knowledge base of stable functional groups. Therefore, it might not be necessary to explicitly model the water environment, and less expensive computational approaches (such as DFT calculations in conjunction with NEB calculations as in Ref.…”

“…A good understanding of the factors that affect the surface dipole in the presence of water may also provide additional insights into the photoelectrode's photocorrosion resistance since there is some evidence of the influence of the surface dipole on photocorrosion reaction pathways (Section 2). These calculations also need to be extended to other functional groups and semiconductor surfaces such as polar surface terminations or iono‐covalent materials such as III–V semiconductors with the goal of obtaining widely applicable design rules.…”

“…Thus, in addition to favorable band‐edge alignment, the PEC device efficiency is also affected by the photoelectrode's stability in aqueous solution, barrier height for charge separation, and catalytic activity . These properties may be optimized by making modifications to the photoelectrode/electrolyte interface …”

Photoelectrochemical study of p-GaP(100)|ZnO|AuNP devices: strategies for enhanced electron transfer and aqueous catalysis

“…[7][8][9] The semiconductor gallium phosphide (GaP, 2.26 eV) has shown promise as both a photocathode 10 and photoanode [11][12][13][14][15] in PEC design. Both materials 14,16,17 and molecular [18][19][20][21] approaches have been used to manipulate the GaP surface, resulting in enhanced passivation and performance. Gallium phosphide based PECs have been used in PECs to afford water oxidation, 10 proton reduction, 11,12,[22][23][24] and -of particular promise -CO 2 reduction.…”