Cobalt-bilayer catalyst decorated Ta3N5 nanorod arrays as integrated electrodes for photoelectrochemical water oxidation

Abstract

Ta 3 N 5 nanorod arrays were fabricated by nitridation of fluorine-containing tantalum oxide (F-Ta 2 O 5 ) nanorod arrays grown in situ on Ta substrates by a one-pot vapour-phase hydrothermal induced selfassembly technique. In this protocol, the in situ generation and the morphology of arrays elaborately adjusted by reaction time, play a vital role in the formation of the F-Ta 2 O 5 nanorod arrays and a highly conductive interlayer between the nanorods and the substrate. Due to the shape anisotropy, ordered hierarchical structure and high surface area, a high photoelectrochemical activity was achieved by the optimum Ta 3 N 5 nanorod photoelectrode with a photocurrent density of 1.22 mA cm À2 under AM 1.5G irradiation at 1.23 V vs. RHE (reversible hydrogen electrode). Furthermore, a higher and more stable photocurrent was demonstrated by combining the highly active Ta 3 N 5 nanorods with stable Co 3 O 4 / Co(OH) 2 (Co 3 O 4 /Co(II)) bilayer catalysts when compared with that demonstrated for Co(II)/Ta 3 N 5 and Co 3 O 4 /Ta 3 N 5 photoelectrodes, exhibiting that not only is the onset potential negatively shifted but also the photocurrent and the stability are significantly improved, which is correlated to an order of magnitude reduction in the resistance to charge transfer at the Ta 3 N 5 /H 2 O interface. Specifically, about 92% of the initial stable photocurrent remains after long-term irradiation at 1.23 V vs. RHE. At 1.23 V vs. RHE, the photocurrent density of Co 3 O 4 /Co(II)/Ta 3 N 5 arrays reached 3.64 mA cm À2 under AM 1.5G simulated sunlight at 100 mW cm À2 , and a maximum IPCE of 39.5% was achieved at 440 nm. This combination of catalytic activity, stability, and conformal decoration makes this a promising approach to improve the photoelectrochemical performance of photoanodes in the general field of energy conversion. Broader contextPhotoelectrochemical (PEC) water splitting based on semiconductor materials is a promising approach to harvest and store solar energy and may have the potential to supply the world's energy demand with a clean and sustainable chemical fuel. Tantalum nitride (Ta 3 N 5 ) is an attractive photoanode material due to its high theoretical solar-to-hydrogen efficiency (15.9% under AM 1.5G illumination), suitable valence band positions for water oxidation, excellent stability, and low material cost. However, it is a challenge to design stable structures that can be used as anodes in the photoelectrochemical cells. In this work, we create the rst Co 3 O 4 /Co(II)/Ta 3 N 5 nanorod array photoanode with a better photoelectrochemical performance to perform water oxidation and generate photocurrent. This strategy as a promising avenue provides new insights into the design and tailoring of tantalum nitride to enhance the photoelectrochemical performance of photoanodes in the general eld of energy conversion.

Strongly Enhanced Water Splitting Performance of Ta3N5 Nanotube Photoanodes with Subnitrides

“…[ 10,[12][13][14][15][16] These factors are benefi cial for the incident light absorption and enhanced PEC water splitting effi ciency of Ta 3 N 5 photoelectrodes. The overall composition of the nitride layer was estimated as Ta 3− x N 5− y O y (i.e., implying the presence of subnitrides).…”

“…[ 15b,c ] The thickness of aligned NT layers could be controlled from 300 nm to several micrometers (>10 µm) with a tube wall (10-50 nm) compared to 300-700 nm layer thickness of NR structures. [10][11][12][13][14][15][16] These 1D nanostructures possess advantages for PEC water splitting, such as an enlarged surface area, small radial size (i.e., facilitating the transportation of minority charge carriers to the solid-liquid interface without recombination), and a high aspect ratio (i.e., a long axial length enabling a maximum absorption of incident light). Particularly, for the water oxidation reaction of the bare Ta 3 N 5 NT photoelectrodes, the photocurrent can reach up to 4.0-5.3 mA cm −2 at 1.6 V RHE in 1 M NaOH under AM 1.5G illumination, [ 16 ] while only ≈2.0 mA cm −2 is obtained for the NRs under the same conditions.…”

“…Since the pioneering work by Fujishima and Honda on a TiO 2 photoanode, [ 1a ] numerous semiconductors have been explored as light absorbers of photoelectrodes in PEC water splitting cells, with the goal of developing low-cost and stable photoelectrodes with a solar to hydrogen conversion effi ciency of over 10%. [10][11][12][13][14][15][16] These 1D nanostructures possess advantages for PEC water splitting, such as an enlarged surface area, small radial size (i.e., facilitating the transportation of minority charge carriers to the solid-liquid interface without recombination), and a high aspect ratio (i.e., a long axial length enabling a maximum absorption of incident light). [6][7][8][9] Effective strategies to improve the photocatalytic activities of Ta 3 N 5 photoanodes are frequently based on morphology control and nanostructuring.…”

Ta3N5-Pt nonwoven cloth with hierarchical nanopores as efficient and easily recyclable macroscale photocatalysts

“…Among semiconductor photocatalysts, Ta 3 N 5 with a narrow band gap of approximately 2.1 eV can absorb and utilize a large fraction of visible light up to 600 nm, and Ta 3 N 5 nanomaterials26272829 and/or films303132333435 have been prepared as visible-light-driven (VLD) photocatalysts. Herein, by using Ta 3 N 5 as a model semiconductor, we report the design and preparation of Ta 3 N 5 -Pt nonwoven cloth that is composed of nanofibers constructed from Ta 3 N 5 nanoparticles, hierarchical nanopores and Pt nanoparticles.…”

Microstructure Effects on the Water Oxidation Activity of Co3O4/Porous Silica Nanocomposites

“…11 Cobalt oxide-decorated gold 12 or graphene 13 electrodes show some of the best catalytic performance in oxygen reduction and evolution reactions, whereas Co 3 O 4 -modified Ta 3 N 5 photoanodes show enhanced performance and stability. 14,15 Co(II)-modified, fluorine-doped tin oxide has high catalytic activity, 16 as do self-repairing cobalt phosphate films 17 and diamondsupported Co 2 O 3 nanoparticles. 18 Mesoporous Co 3 O 4 prepared by hard-templating methods show increased stability and electrocatalytic ability.…”