Abstract
The lack of active, stable, earth-abundant, and visible-light absorbing materials to replace plasmonic noble metals is a critical obstacle for researchers in developing highly efficient and cost-effective photocatalytic systems. Herein, a core–shell nanotube catalyst was fabricated consisting of atomic layer deposited HfN shell and anodic TiO2 support layer with full-visible regime photoactivity for photoelectrochemical water splitting. The HfN active layer has two unique characteristics: (1) A large bandgap between optical and acoustic phonon modes and (2) No electronic bandgap, which allows a large population of long life-time hot carriers, which are used to enhance the photoelectrochemical performance. The photocurrent density (≈2.5 mA·cm−2 at 1 V vs. Ag/AgCl) obtained in this study under AM 1.5G 1 Sun illumination is unprecedented, as it is superior to most existing plasmonic noble metal-decorated catalysts and surprisingly indicates a photocurrent response that extends to 730 nm. The result demonstrates the far-reaching application potential of replacing active HER/HOR noble metals such as Au, Ag, Pt, Pd, etc. with low-cost plasmonic ceramics.
Highlights
The group IV transition metal nitrides are beginning to attract a great deal of attention due to their unique characteristics such as exhibiting both metallic and semiconducting properties, possessing ceramic hardness, high thermal tolerance, and chemical resistance, showing the possibility for substitution of plasmonic noble metal, etc. [1,2]
After being dried under a nitrogen stream, the top 3 mm of each substrate was covered with Kapton tape, which was done to keep an fluorine-doped tin oxide (FTO)-exposed area for contact in later experiments
We reported a method for the fabrication of core–shell nanotube arrays consisting of a 20 nm ALD HfN shell and an anodic TiO2 nanotube support layer
Summary
The group IV transition metal nitrides are beginning to attract a great deal of attention due to their unique characteristics such as exhibiting both metallic and semiconducting properties, possessing ceramic hardness, high thermal tolerance, and chemical resistance, showing the possibility for substitution of plasmonic noble metal, etc. [1,2]. Based on the findings from pioneer studies, HfN is worth investigating as a photocatalyst for solar energy conversion due to the following reasons: (1) high thermal and chemical resistance, and photochemical stability under harsh conditions; (2) long hot carrier lifetime; (3) plasmon resonance in the Vis-NIR regime; and (4) cost-efficient alternative to noble metals. Despite the aforementioned properties that are beneficial to photocatalytic energy conversion, no one has reported the successful utilization of HfN for any kind of photocatalytic reactions With this aim in mind, a photoanode consisting of TiO2(core)–HfN(shell) nanotube arrays (HfN-TNT) was deployed in photoelectrochemical water splitting and achieved a champion photocurrent of 2.48 mA·cm−2 under 1 Sun illumination (AM 1.5G) at an applied bias of +0.6 V vs Ag/AgCl reference electrode in 1 M KOH solution. The catalyst is economically efficient and suitable for large-scale production due to the scalability and existing industrial usage of electrochemical anodization and atomic layer deposition
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