Covalently Grafting Graphene onto Si Photocathode to Expedite Aqueous Photoelectrochemical CO₂ Reduction

Abstract

Silicon semiconductor functionalized with molecular catalysts emerges as a promising cathode for photoelectrochemical (PEC) CO 2 reduction reaction (CO 2 RR). However, the limited kinetics and stabilities remains a major hurdle for the development of such composites. We herein report an assembling strategy of silicon photocathodes via chemically grafting a conductive graphene layer onto the surface of n + -p Si followed by catalyst immobilization. The covalently-linked graphene layer effectively enhances the photogenerated carriers transfer between the cathode and the reduction catalyst, and improves the operating stability of the electrode. Strikingly, we demonstrate that altering the stacking configuration of the immobilized cobalt tetraphenylporphyrin (CoTPP) catalyst through calcination can further enhance the electron transfer rate and the PEC performance. At the end, the graphene-coated Si cathode immobilized with CoTPP catalyst managed to sustain a stable 1-Sun photocurrent of À 1.65 mA cm À 2 over 16 h for CO production in water at a near neutral potential of À 0.1 V vs. reversible hydrogen electrode. This represents a remarkable improvement of PEC CO 2 RR performance in contrast to the reported photocathodes functionalized with molecular catalysts.

Covalently Linking Reduced Graphene Oxide Facilitated Electrodeposition of MoS2 on Silicon Pyramidal Photocathode To Enhance Hydrogen Evolution

“…The elemental mapping results (Figure j) show the distribution of MoS 2 on Si/rGO, and the corresponding energy-dispersive X-ray (EDX) spectrum (Figure S2) verifies that Si/rGO/MoS 2 is composed of Si, C, O, Mo, and S. As indicated in the infrared spectra (Figure a), a hydroxyl-rich Si surface can be obtained after Piranha solution treatment. A much stronger peak appears at about 3380 cm –1 , indicating more hydroxyl groups have been modified onto the Si surface after the esterification reaction . Raman spectra of Si/rGO/MoS 2 show characteristic peaks of rGO (Figure b).…”

Tailoring co-catalysts on Si photocathodes for efficient photoelectrochemical CO2 reduction: recent progress and prospects of deposition methods

“…Additionally, it reached a maximum partial current density of −4 mA cm −2 at −0.4 V (vs. RHE) for CO generation. 99 Zheng et al reported the sequential fabrication of the p-Si/ n-ZnO v /p-Cu x O nanostructure using chemical methods, involving the replacement of Zn with Cu. The resulting p-Si/n-ZnO v / p-Cu x O structure demonstrated exceptional PEC CO 2 RR selectivity towards ethanol at low biases, achieving an outstanding FE of approximately 60% at 0 V vs. RHE.…”

“…Additionally, it reached a maximum partial current density of −4 mA cm −2 at −0.4 V ( vs. RHE) for CO generation. 99…”

Photoelectrocatalytic Utilization of CO2: A Big Show of Si‐based Photoelectrodes

“…To further facilitate the charge transfer between Si and graphene, Wei et al grafted graphene directly onto the Si surface via covalent bonding thus avoiding the impediment of TiO 2 interlayer to the charge transfer. [53] The homogeneous catalyst cobalt tetraphenylporphyrin (CoTPP) was immobilized on the surface of graphene via π-π stacking interaction. An onset potential of ~0.1 V (vs. RHE) was finally achieved for PEC CO 2 reduction, with a maximum partial current density of ~À 4 mA cm À 2 at À 0.4 V (vs. RHE) for CO production.…”