Porous rod-like Ni 2 P/Ni assemblies for enhanced urea electrooxidation
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hool of Chemistry and Chemical Engineering, Yangzhou University, Yangzhou 225009, China Guangling College, Yangzhou University, Yangzhou 225009, China 3 Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, China 2
© Tsinghua University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020 Received: 17 September 2020 / Revised: 9 October 2020 / Accepted: 15 October 2020
ABSTRACT The urea oxidation reaction has attracted increasing attention. Here, porous rod-like Ni2P/Ni assemblies, which consist of numerous nanoparticle subunits with matching interfaces at the nanoscale have been synthesized via a simple phosphating approach. Density functional theory calculations and density of states indicate that porous rod-like Ni2P/Ni assemblies can significantly enhance the activity of chemical bonds and the conductivity compared with NiO/Ni toward the urea oxidation reaction. The optimal catalyst of Ni2P/Ni can deliver a low overpotential of 50 mV at 10 mA·cm−2 and Tafel slope of 87.6 mV·dec−1 in urea oxidation reaction. Moreover, the constructed electrolytic cell exhibits a current density of 10 mA·cm−2 at a cell voltage of 1.47 V and an outstanding durability in the two-electrode system. This work has provided a new possibility to fabricate metal phosphides-metal assemblies with advanced performance.
KEYWORDS rod-like Ni2P/Ni, electrocatalyst, urea electrooxidation, overall urea electrolysis
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Introduction
A growing number of studies suggest that, for efficient electrolysis in alkaline solutions, nickel-based materials have great potential to replace precious metals (such as Pt, Rh, Au, etc.), which are outstanding electrode materials in electrocatalysis, though suffering from high cost and their scarcity [1–8]. Notably, it is still a great challenge to develop the electroactive sites, reactivity, and stability of the electrocatalytic materials for their full usage [9–14]. Among the nickel-based materials, nickel phosphide (Ni2P) and its composites have recently emerged as a candidate for urea oxidation reaction (UOR) because of their high catalytic ability [15–19]. Wang et al. [10] demonstrated the essentiality of Ni2+/Ni3+ in the oxidation reaction by in situ Raman spectroscopy, analyzing its mechanism. Because Ni2+ oxidizes to Ni3+ more easily before the reaction starts, more electroactive sites will be obtained [20–22]. Compared with NiO, which is a typical electrocatalytic material for UOR, the energy of Ni2P is significantly lower, because of the lower energy of the Ni–P bond compared to that of Ni–O [23–25]. Nevertheless, the weak stability hinders its wide application. Fortunately, composites made of Ni2P and other materials can solve this issue by synergistically combining the properties of the materials [26–28]. Therefore, considering the feasibility of the synthesis, the composites of Ni2P and appropriate materials may provide suitable candidates as electrocatalysts for the UOR. At present, hydrogen fuel has been considered as great potential ca
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