Recent Development of Nickel-Based Electrocatalysts for Urea Electrolysis in Alkaline Solution

Abstract

Recently, urea electrolysis has been regarded as an up-and-coming pathway for the sustainability of hydrogen fuel production according to its far lower theoretical and thermodynamic electrolytic cell potential (0.37 V) compared to water electrolysis (1.23 V) and rectification of urea-rich wastewater pollution. The new era of the “hydrogen energy economy” involving urea electrolysis can efficiently promote the development of a low-carbon future. In recent decades, numerous inexpensive and fruitful nickel-based materials (metallic Ni, Ni-alloys, oxides/hydroxides, chalcogenides, nitrides and phosphides) have been explored as potential energy saving monofunctional and bifunctional electrocatalysts for urea electrolysis in alkaline solution. In this review, we start with a discussion about the basics and fundamentals of urea electrolysis, including the urea oxidation reaction (UOR) and the hydrogen evolution reaction (HER), and then discuss the strategies for designing electrocatalysts for the UOR, HER and both reactions (bifunctional). Next, the catalytic performance, mechanisms and factors including morphology, composition and electrode/electrolyte kinetics for the ameliorated and diminished activity of the various aforementioned nickel-based electrocatalysts for urea electrolysis, including monofunctional (UOR or HER) and bifunctional (UOR and HER) types, are summarized. Lastly, the features of persisting challenges, future prospects and expectations of unravelling the bifunctional electrocatalysts for urea-based energy conversion technologies, including urea electrolysis, urea fuel cells and photoelectrochemical urea splitting, are illuminated.

Indirect urea electrooxidation by nickel(III) in alkaline medium: From kinetic and mechanism to reactor modeling

“…This low value suggests that the kinetic rate slightly depends on the urea concentration, which can be explained by these assumptions: (i)the strong affinity of urea to the nickel peroxide particles. Several works have studied the adsorption of urea molecules on various adsorbents: nickel(II) oxide NiO, 43 nickel nanoparticles embedded in carbon nanotubes, 44 and nickel(III) sites 45 . Whatever the adsorbent nature, a strong affinity of urea with nickel 43 and a low adsorption energy of urea 46 have been reported.…”

Asymmetric Coordination Environment Engineering of Atomic Catalysts for CO2 Reduction

“…In addition, the factor of long-term thermodynamic stability also needs to be considered [ 204 , 205 ]. Too strong or too weak interactions in the metal-species-anchored supports systems during catalysis can result in negative Ostwald maturation and the migration and aggregation of active sites, respectively [ 206 , 207 ]. In particular, the high temperatures and reducing environments usually faced in industrial applications make catalysts more vulnerable to poisoning or deactivation [ 199 , 207 ].…”

“…Too strong or too weak interactions in the metal-species-anchored supports systems during catalysis can result in negative Ostwald maturation and the migration and aggregation of active sites, respectively [ 206 , 207 ]. In particular, the high temperatures and reducing environments usually faced in industrial applications make catalysts more vulnerable to poisoning or deactivation [ 199 , 207 ]. Overall, the design of high-quality asymmetric atom electrocatalysts via reasonable coordination modulation remains promising.…”

In Situ X‐ray Absorption Spectroscopy of Metal/Nitrogen‐doped Carbons in Oxygen Electrocatalysis

“…Among earth-abundant transition metals, nickel (Ni) is one of the most favorable oxygen-evolving catalysts due to its desirable electrocatalytic activity and stability in alkaline electrolyte solutions. [9,96] Even though tremendous progress has been achieved in the past decade in the improvement of electrochemical performance of NiÀ NÀ C-based oxygen catalysts, fundamental understanding of the structural dynamics and active sites of the electrocatalyst is still lacking. [12] In situ XAS has been employed to study electrocatalytic OER mechanisms by allowing the elucidation of the local atomic and electronic structure of the given element under reaction conditions, [2] which makes possible the exploration of scalable methods to synthesize high-performance NiÀ NÀ C materials for oxygen electrocatalysis.…”

“…Among earth‐abundant transition metals, nickel (Ni) is one of the most favorable oxygen‐evolving catalysts due to its desirable electrocatalytic activity and stability in alkaline electrolyte solutions [9, 96] . Even though tremendous progress has been achieved in the past decade in the improvement of electrochemical performance of Ni−N−C‐based oxygen catalysts, fundamental understanding of the structural dynamics and active sites of the electrocatalyst is still lacking [12] .…”