Hierarchical Structure of CuO Nanowires Decorated with Ni(OH)₂ Supported on Cu Foam for Hydrogen Production via Urea Electrocatalysis

Abstract

Owing to the low theoretical potential of the urea oxidation reaction (UOR), urea electrolysis is an energy‐saving technique for the generation of hydrogen. Herein, a hierarchical structure of CuO nanowires decorated with nickel hydroxide supported on 3D Cu foam is constructed. Combined theoretical and experimental analyses demonstrate the high reactivity and selectivity of CuO and Ni(OH)2 toward the UOR instead of the oxygen evolution reaction. The hierarchical structure creates a synergistic effect between the two highly active sites, enabling an exceptional UOR activity with a record low potential of 1.334 V (vs the reversible hydrogen electrode) to reach 100 mA cm−2 and a low Tafel slope of 14 mV dec−1 in 1 m KOH and 0.5 m urea electrolyte. Assembling full urea electrolysis driven by this developed UOR electrocatalyst as the anode and a commercial Pt/C electrocatalyst as the cathode provides a current density of 20 mA cm−2 at a cell voltage of ≈1.36 V with promising operational stability for at least 150 h. This work not only enriches the UOR material family but also significantly advances energy‐saving hydrogen production.

Hierarchical Ni–Mo–P nanoarrays toward efficient urea oxidation reaction

“…4,5 In this case, replacing the unsatisfactory OER with alternative oxidation reactions endowed with a lower thermodynamic voltage and coupling with the HER can reduce the applied overpotential and enhance the energy conversion efficiency of hydrogen production, such as the oxidation reactions of methanol, urea, and hydrazine. 6,7 In particular, urea, which widely exists in industrial and agriculture sewage, is a promising substitute for water owing to its ultralow theoretical potential of 0.37 V. Thus, coupling the urea oxidation reaction with the HER is expected to achieve energy-saving hydrogen production and waste water purification. 8,9 However, despite its low thermodynamic voltage, the UOR is a complex process (CO (NH 2 ) 2 + 6OH − → N 2 + 5H 2 O + CO 2 + 6e − ), which also suffers from sluggish kinetics due to its 6e − -transfer step and requires highly efficient and affordable catalysts to drive the electrocatalytic urea oxidation reaction.…”

One Bifunctional Electrocatalyst Derived from Nickel MOF for Urea Oxidation Reaction and Hydrogen Evolution Reaction

“…Among them, methane hydrogen production requires energy consumption and also produces pollutants. Electrolysis of water to make hydrogen is currently another common method for hydrogen production; in the water electrolysis reaction, there are hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), of which a larger potential is demanded for the anodic OER . The result will also lead to energy consumption, thus limiting the rate of hydrogen production.…”

“…Electrolysis of water to make hydrogen is currently another common method for hydrogen production; 8 in the water electrolysis reaction, there are hydrogen evolution reaction (HER) 9 and oxygen evolution reaction (OER), 10 of which a larger potential is demanded for the anodic OER. 11 The result will also lead to energy consumption, thus limiting the rate of hydrogen production. Therefore, it is necessary to find electrocatalysts that can accelerate the OER or replace OER with other oxidation reactions.…”

In situ phase-reconfiguration to synthesize Ru, B co-doped nickel phosphide for energy-efficient hydrogen generation in alkaline electrolytes

“…However, relative to the 4e À transfer mechanism (4OH À / 2H 2 O + O 2 + 4e À ), 33,34 the UOR involves more complex 6e À transfer (CO(NH 2 ) 2 + 6OH À / N 2 + 5H 2 O + CO 2 + 6e À ) and generates complex gases containing N 2 and CO 2 . [35][36][37] Thus, the UOR is still affected by complex electron transfer and adsorption/desorption of various intermediates, leading to intrinsically slow kinetics. Hence, developing highly active catalysts is the key factor in the practical applications of the above energy-saving strategy to generate hydrogen energy.…”