Hybridization
of homogeneous catalytic sites with a photoelectrode
is an attractive approach to highly selective and tunable photocatalysis
using heterogeneous platforms. However, weak and unclear surface chemistry
often leads to the dissociation and irregular orientation of catalytic
centers, restricting long-term usability with high selectivity. Well-defined
and robust ligands that can persist under harsh photocatalytic conditions
are essential for the success of hybrid-type photocatalysis. Here,
we introduce N-heterocyclic carbene as a durable linker for the immobilization
of a Rubpy complex-based CO2 reduction site (cis-dichloro-(4,4′-diphosphonato-Rubpy)(p-cymene)
(RuCY)) on a p-type gallium nitride/gold nanoparticle (p-GaN/AuNP)
heterostructure. The p-GaN/AuNPs/RuCY photocathode was coupled with
a hematite photoanode to drive photoelectrochemical CO2 reduction along with water oxidation. Highly selective CO2 reduction into formates, up to 98.2%, was achieved utilizing plasmonic
hot electrons accumulated on AuNPs. The turnover frequency was 1.46
min–1 with a faradic efficiency of 96.8% under visible
light illumination (243 mW·cm–2). This work
demonstrates that the N-heterocyclic carbene-mediated surface functionalization
with homogeneous catalytic sites is a promising approach to increase
the sustainability and usability of hybrid catalysts.
Plasmonic water splitting gains increasing attention due to their broad absorption spectra and excellent chemical stability. However, plasmonic water splitting suffers from low efficiency due to difficulties of utilizing plasmonic energetic charge carriers. Structural factors need to be carefully examined to overcome the short lifetime of plasmonic hot carriers. Here we investigate Au/TiO 2 half-dome patterns as a plasmonic photoelectrode to examine the effects of incident light angle and orientation of nanostructures on photochemical hydrogen evolution. Half-dome structures exhibit 4-and 3-fold higher photocurrent density and photovoltage, respectively, than a flat thin film. The enhanced photoreactivity is ascribed to the increased angle between the Au/TiO 2 interface and the electric field of irradiated light. The result indicates that the kinetic momentum of the incident photon can significantly contribute to hot electron injection and reaction rate. The monolithic Au/ TiO 2 /Pt half-dome structures are also constructed to show sustainable hydrogen evolution without external bias under visible light illumination.
Highlights
MoP nanorod-array catalysts were directly synthesized on graphene passivated silicon photocathodes without secondary phase.
Mo-O-C covalent bondings and energy band bending at heterointerfaces facilitate the electron transfer to the reaction sites.
Numerous catalytic sites and drastically enhanced anti-reflectance of MoP nanorods contribute to the high solar energy conversion efficiency.
Abstract
Transition metal phosphides (TMPs) and transition metal dichalcogenides (TMDs) have been widely investigated as photoelectrochemical (PEC) catalysts for hydrogen evolution reaction (HER). Using high-temperature processes to get crystallized compounds with large-area uniformity, it is still challenging to directly synthesize these catalysts on silicon photocathodes due to chemical incompatibility at the heterointerface. Here, a graphene interlayer is applied between p-Si and MoP nanorods to enable fully engineered interfaces without forming a metallic secondary compound that absorbs a parasitic light and provides an inefficient electron path for hydrogen evolution. Furthermore, the graphene facilitates the photogenerated electrons to rapidly transfer by creating Mo-O-C covalent bondings and energetically favorable band bending. With a bridging role of graphene, numerous active sites and anti-reflectance of MoP nanorods lead to significantly improved PEC-HER performance with a high photocurrent density of 21.8 mA cm−2 at 0 V versus RHE and high stability. Besides, low dependence on pH and temperature is observed with MoP nanorods incorporated photocathodes, which is desirable for practical use as a part of PEC cells. These results indicate that the direct synthesis of TMPs and TMDs enabled by graphene interlayer is a new promising way to fabricate Si-based photocathodes with high-quality interfaces and superior HER performance.
Graphic Abstract
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