Abstract
The use of hematite as the photoanode for photoelectrochemical hydrogen production by solar energy has been actively studied due to its abundance, stability, and adequate optical properties. Deposition of an electrocatalyst overlayer on the hematite may increase kinetics and lower the onset potential for water splitting. NixFe1−xOy is one of the most effective electrocatalysts reported for this purpose. However, the condition and results of the previous reports vary significantly, and a comprehensive model for NixFe1−xOy/hematite is lacking. Here, we report a simple and novel chemical bath deposition method for depositing low-onset-potential NixFe1−xOy electrocatalyst on hematite. With a Ni percentage of 80% and an immersion time of 2 min, the as-prepared NixFe1−xOy overlayer raised the photovoltage from 0.2 V to 0.7 V, leading to a cathodic shift of the onset potential by 400 mV, while maintaining the same level of current density. The dependence of the electrochemical and photoelectrochemical characteristics of the photoanode on the condition of the electrocatalyst was studied systematically and explained based on energy level diagrams and kinetics.
Highlights
Sunlight-driven photoelectrochemical water splitting is one of the promising methods for converting solar energy to chemical energy without emission of CO2 [1,2,3]
The photovoltage represents the capability of the photoanode to perform photo-assisted water splitting, and the increase in photovoltage normally results in a corresponding reduction in the onset potential for water splitting
It is shown in this work that deposition of Nix Fe1− x Oy electrocatalyst on hematite in order to produce a low-onset-potential photoanode for solar hydrogen production can be attained by a simple room-temperature chemical bath deposition method
Summary
Sunlight-driven photoelectrochemical water splitting is one of the promising methods for converting solar energy to chemical energy without emission of CO2 [1,2,3]. To achieve this goal with high efficiency, materials used in water splitting devices should be naturally abundant, have high absorbance for solar radiation, possess proper energy level positions and fast kinetics for oxygen evolution reaction or hydrogen evolution reaction, and must be stable under the harsh working conditions. Nanostructured hematite holds great promise in many aspects, its inadequate surface state energy level results in a low photovoltage and a high onset potential for water splitting Further improvement of the efficiency of hematite photoanode by nanostructuring and intrinsic doping [13,19] or extrinsic doping [15,16,17,18,19] has been actively pursued.
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