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Urea electrolysis can address pressing environmental concerns caused by urea-containing wastewater while realizing energy-saving hydrogen production. Highly efficient and affordable electrocatalysts are indispensable for realizing the great potential of this emerging technology. Among the numerous candidates, α-Ni(OH)2has the merits of good electrocatalytic activity, adjustable heteroelement doping, and low cost; consequently, it has received tremendous attention in the electrolytic fields. Herein, a Y3+-doping strategy is developed to effectively enhance the catalytic performance of nickel hydroxide in the urea oxidation reaction (UOR). Our results show that Y3+incorporation successfully modulates the electronic structure of α-Ni(OH)2by inducing Ni3+formation in the crystal lattice to initiate direct UOR, facilitates the Ni3+/Ni2+redox transition with higher current responses to promote indirect UOR, and maintains the structural stability of YNi-10 (Ni2+/Y3+molar ratio = 1:0.1) during long-term UOR operation. Owing to these features, the obtained YNi-10 sample exhibits a higher current density (127 vs 79 mA cm–2at 1.5 V), a lower Tafel slope (48 vs 75 mV dec–1), a larger potential difference between the UOR and oxygen evolution reaction (OER, 0.26 vs 0.22 V at 80 mA cm–2), a higher reaction rate constant (1.1 × 105vs 3.1 × 103cm3mol–1s–1), and a reduced activation energy of UOR (2.9 vs 14.8 kJ mol–1) compared with the Y-free counterpart (YNi-0). This study presents a promising strategy to simultaneously boost direct and indirect UORs, providing new insights for further developing high-performance electrocatalysts.

Ni(OH)2shows great promise as an electrocatalyst for the urea oxidation reaction (UOR), which can be employed in energy conversion devices such as direct urea fuel cells. The stacking of nickel hydroxide layers with different chemistries results in diverse crystal structures of nickel hydroxide. Compared to the β phase, α-Ni(OH)2allows more than one electron transfer during redox transition, which is beneficial to energy conversion applications. This study reveals that the synthesized α-Ni(OH)2electrocatalyst exhibits higher current responses (increased by 138% at 1.5 V vs.RHE), a lower slope in the Tafel plot (89 vs.121 mV dec−1), and an improved reaction rate constant (increased by 290%) for the UOR in comparison with its nickel hydroxide counterpart (i.e., β-Ni(OH)2). Moreover, quantitative analyses based on the normalized current responses with respect to the double-layer electrochemical surface area of the nickel hydroxide electrodes indicate the higher intrinsic UOR catalytic activity of the α-Ni(OH)2catalyst. More importantly, the α-Ni(OH)2catalyst exhibits superior stability toward urea electrolysis in a 20 000 s test without noticeable degradation of the catalyst.