Water splitting has been regarded as a sustainable and environmentally-friendly technique to realize green hydrogen generation, while more energy is consumed due to the high overpotentials required for the anode oxygen evolution reaction. Urea electrooxidation, an ideal substitute, is thus received increasing attention in assisting water-splitting reactions. Note that highly efficient catalysts are still required to drive urea oxidation, and the facile generation of high valence state species is significant in the reaction based on the electrochemical-chemical mechanisms. The high cost and rareness make the noble metal catalysts impossible for further consideration in large-scale application. Ni-based catalysts are very promising due to their cheap price, facile structure tuning, good compatibility, and easy active phase formation. In the light of the significant advances made recently, herein, we reviewed the recent advances of Ni-based powder catalysts for urea oxidation in assisting water-splitting reaction. The fundamental of urea oxidation is firstly presented to clarify the mechanism of urea-assisted water splitting, and then the prevailing evaluation indicators are briefly expressed based on the electrochemical measurements. The catalyst design principle including synergistic effect, electronic effect, defect construction and surface reconstruction as well as the main fabrication approaches are presented and the advances of various Ni-based powder catalysts for urea assisted water splitting are summarized and discussed. The problems and challenges are also concluded for the Ni-based powder catalysts fabrication, the performance evaluation, and their application. Considering the key influencing factors for catalytic process and their application, attention should be given to structure−property relationship deciphering, novel Ni-based powder catalysts development and their construction in the real device; specifically, the effort should be directed to the Ni-based powder catalyst with multi-functions to simultaneously promote the fundamental steps and high anti-corrosion ability by revealing the local structure reconstruction as well as the integration in the practical application. We believe the current summarization will be instructive and helpful for the Ni-based powder catalysts development and understanding their catalytic action for urea-assisted hydrogen generation via water splitting technique. Advances and challenges of Ni based powder catalyst were reviewed for urea oxidation in assisting water-splitting reaction. 

A review of Ni based powder catalyst for urea oxidation in assisting water splitting reaction

With the development of renewable energy systems, clean hydrogen is burgeoning as an optimal alternative to fossil fuels, in which its application is promising to retarding the global energy and environmental crisis. The hydrogen evolution reaction (HER), capable of producing high-purity hydrogen rapidly in electrocatalytic water splitting, has received much attention. Abundant research about HER has been done, focusing on advanced electrocatalyst design with high efficiency and robust stability. As potential HER catalysts, metal nanoclusters (MNCs) have been studied extensively. They are composed of several to a hundred metal atoms, with sizes being comparable to the Fermi wavelength of electrons, that is, < 2.0 nm. Different from metal atoms/nanoparticles, they exhibit unique catalytic properties due to their quantum size effect and low-coordination environment. In this review, the activity-enhancing approaches of MNCs applied in HER electrocatalysis are mainly summarized. Furthermore, recent progress in MNCs classified with different stabilization strategies, that is, the freestanding MNCs, MNCs with organic, metal and carbon supports, are introduced. Finally, the current challenges and deficiencies of these MNCs for HER are prospected.

Advances in the Electrocatalytic Hydrogen Evolution Reaction by Metal Nanoclusters-based Materials.

Urea electrooxidation has received considerable attention because of its tremendous practical application in environmental protection and energy regeneration. As an electrochemical reaction, the catalytic performance of urea oxidation is highly...

A review of hetero-structured Ni-based active catalysts for urea electrolysis

Hierarchical NiCo2O4/CuO-C Nanocomposite Derived from Copper-Based Metal Organic Framework and Ni/Co Hydroxides: Excellent Electrocatalytic Activity Towards Methanol Oxidation

Nickel nanocrystal/sulfur-doped Carbon Composites as Efficient and Stable Electrocatalysts for Urea Oxidation Reaction

3D nickel diselenide architecture on nitrogen-doped carbon as a highly efficient electrode for the electrooxidation of methanol and urea

Design and synthesis of electrocatalysts with high activity and low cost is an important challenge for water splitting. We report a rapid and facile synthetic route to obtain IrxNi clusters via polyol reduction. The IrxNi clusters show excellent activity for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in acidic electrolytes. The optimized Ir2Ni/C clusters exhibit an electrochemical active area of 18.27 mF cm−2, with the overpotential of OER being 292 mV and HER being 30 mV at 10 mA cm−2, respectively. In addition, the Ir2Ni/C used as the cathode and anode for the H-type hydrolysis tank only needs 1.597 V cell voltages. The excellent electrocatalytic performance is mainly attributed to the synergistic effect between the metals and the ultra-fine particle size. This study provides a novel strategy that has a broad application for water splitting.

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Jingchun Jia

Papers

3D nickel diselenide architecture on nitrogen-doped carbon as a highly efficient electrode for the electrooxidation of methanol and urea

Ultradispersed IrxNi clusters as bifunctional electrocatalysts for high-efficiency water splitting in acid electrolytes

Controlled assembly of nitrogen-doped iron carbide nanoparticles on reduced graphene oxide for electrochemical reduction of carbon dioxide to syngas

Fe−Ni Nanoparticles on N-doped Carbon as Catalysts for Electrocatalytic Reduction of CO2 to Tune CO/H2 Ratio