Cobalt phosphide nanoarrays with crystalline-amorphous hybrid phase for hydrogen production in universal-pH
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TRACT To accomplish mass hydrogen production by electrochemical water-splitting, it is a necessary to develop robust, highly active, stable, and cost-effective hydrogen evolution reaction (HER) electrocatalysts that perform comparably to Pt in the universal pH range. In this work, cobalt phosphide hybrid nanosheets supported on carbon felt (CoP HNS/CF) are presented, which exhibit the superior electrocatalytic hydrogen production under a universal-pH. In these nanosheets, a single CoP HNS is composed of polycrystalline CoP and oxygen-enriched amorphous Co-O-P phase. Benefiting from its unique nanoarchitecture, as-fabricated CoP HNS/CF exhibits a tremendous electrocatalytic HER activity and outperforms Pt/C as well as state-of-the-art CoP electrocatalysts in universal-pH. In acidic and neutral media, the CoP HNS/CF shows superior electrocatalytic activity while maintaining its original hybrid crystalline-amorphous phase and morphology. In alkaline medium, the unexpected phase and morphological reorganization of CoP HNS/CF results in outstanding electrocatalytic operation. CoP HNS/CF not only achieves high electrocatalytic activity and kinetics, but also a stable and long operating lifetime even under a high current density of 500 mA·cm−2. Furthermore, the fabrication of CoP HNS/CF can be scaled up easily, and the large CoP HNS/CF electrode also exhibits similar electrocatalytic activity and stability.
KEYWORDS cobalt phosphide, self-supporting, electrocatalyst, hydrogen evolution reaction, universal-pH, large-scale
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Introduction
Global warming and environmental pollution owing to the ever-increasing consumption of fossil fuels have become eminent concerns recently. So, it is now indispensable to develop alternative energy resources [1–4]. Molecular hydrogen (H2) has been proposed as an ideal energy-transfer medium in the fields of transportation as well as stationary applications, due to its high gravimetric energy density (142 MJ·kg−1) and carbon-emission free nature [1, 5–7]. So far hydrogen production by reforming natural gas has been considered as the most economical technique, however, electrochemical water-splitting combined with renewable energy resources is a potential pathway toward eco-friendly, sustainable and large-scale hydrogen production [6, 8–10]. Hydrogen production through water electrolysis primarily requires a highly active electrocatalyst to maximize the overall efficiency [1, 3, 5, 11]. Currently, platinum-on-carbon (Pt/C) is regarded as the most active electrocatalyst for the hydrogen evolution reaction (HER). However, its high cost and natural scarcity restrict its large-scale application [1, 4, 5]. In the past decade, considerable non-noble metal compounds have been researched to overcome these limitations. Among them, transition metal phosphides (TMPs) have been regarded as an attractive candidate for Pt-based electrocatalysts because of their low cost, good intrinsic activity, and stability toward HER in a wide pH range [5, 12, 13]. However, despite numerous efforts to develop TMPs for
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