Cu-Doping Effect on the Electrocatalytic Properties of Self-Supported Cu-Doped Ni₃S₂ Nanosheets for Hydrogen Production via Efficient Urea Oxidation

Abstract

The urea oxidation reaction (UOR) is considered as a substitutable oxidation process to supplant the oxygen evolution reaction (OER) for pure and clean hydrogen generation because of its much lower theoretic thermodynamic onset potential. Preparing heteroatomically doped and self-supported three-dimensional (3D) catalysts has become an efficient pathway to promote the electrochemical performance of catalysts. Recently, Cu-based complexes have been investigated as OER catalysts and exhibited improved catalytic activities. However, Cu-doped composites as UOR catalysts have been rarely reported, and the effect of Cu remains unclear in the UOR process. The present work exhibits a selfsupported electrocatalyst of Cu-doped Ni 3 S 2 nanosheets supported on Ni foam (NF) synthesized via a direct one-step hydrothermal sulfuration method and unlocks the effect of Cu on the relationship between the catalyst structure and UOR performance. The doping of the Cu element transformed the morphology of Ni 3 S 2 from nanoparticles to nanosheets, increasing the active surface area. Meanwhile, the Cu dopant regulated the electronic structure of Cu-doped Ni 3 S 2 by promoting electron transport from the Ni atom to the Cu dopant, stimulating the formation of active Ni sites with a high valency during UOR. Moreover, the doping of the Cu element optimized the Gibbs adsorption energies of the pivotal intermediates during urea oxidation. Remarkably, as-prepared Cu-doped Ni 3 S 2 /NF required only 1.30 V vs RHE toward UOR and an overpotential of 188 mV toward the hydrogen evolution reaction (HER) to deliver 10 mA cm −2 with outstanding electrochemical durability. Besides, the overall urea electrolyzer constructed using Cu-doped Ni 3 S 2 /NF as the UOR and HER catalyst needed only 1.57 V to deliver 10 mA cm −2 with stable durability during a long-term test. The present research offers novel insights into the research for designing and preparing efficient and durable electrodes in urea oxidation applications.

(NiFeCu)3S2@(NiFeCu)O Core-Shelled Heterostructure Having Dual-Anion Vacancies for Stable, High-Efficiency Urea Oxidation Reaction

“…To the best of our knowledge, this new UOR catalyst has not been reported. Fe and Cu are used as dopants because they accelerate the electron transfer from Ni to Fe and/or Cu, thus promoting the formation of high Ni-oxidation state for facile UOR. − Here, we show that the long-term stability is therefore enhanced. The dual anion vacancies of Vs and Vo were found to control the charge transfer and intermediate species adsorption resistance, respectively.…”

Ni2Se3−CuSex Heterostructure as a Highly Efficient Bifunctional Electrocatalyst for Urea‐Assisted Hydrogen Generation

“…In addition, the adsorption energies of the reaction intermediates (H*, NH 2 *, and CO*) may decrease at Ni sites after the introduction of Cu‐based species into the Ni‐based material. Normally, the adsorption energy at the Ni site is lower than that of Cu sites, indicating that Ni atoms act as the main active sites [45,46] . Thus, the prepared Ni 3 Se 2 @CuSe x /CF heterostructure may follow similar catalytic reaction mechanism for HER/UOR.…”

“…Normally, the adsorption energy at the Ni site is lower than that of Cu sites, indicating that Ni atoms act as the main active sites. [45,46] Thus, the prepared Ni 3 Se 2 @CuSe x /CF heterostructure may follow similar catalytic reaction mechanism for HER/UOR.…”

“…The coupling of CuSe x may help to modulate the electronic structure and surface properties of Ni 3 Se 2 for better reaction kinetics. In addition, the underlying mechanism of improved HER and UOR performance by introducing the heterogeneous interfaces, can be summarized according to related Cu−Ni‐based material systems for urea‐assisted water electrolysis [45,46] . For both HER and UOR, the main catalytic active sites are Ni‐based species.…”

“…In addition, the underlying mechanism of improved HER and UOR performance by introducing the heterogeneous interfaces, can be summarized according to related CuÀ Ni-based material systems for ureaassisted water electrolysis. [45,46] For both HER and UOR, the main catalytic active sites are Ni-based species. The incorporation of Cu species contributes to the regulation of electronic structure of Ni-based materials by electron transfer at interfaces.…”