Highly Efficient Urea Oxidation via Nesting Nano-Nickel Oxide in Eggshell Membrane-Derived Carbon

Abstract

Here, we reported a strategy of using an eggshell membrane to produce hierarchically porous carbon as a low-cost substrate for synthesizing nano nickel oxide catalyst (C@NiO), which can effectively turn biowaste -urea into energy through an electrochemical approach. The interwoven carbon networks within NiO led to highly efficient urea oxidation due to the strong synergistic effect. The as-prepared electrode only needed 1.36 V versus reversible hydrogen electrode to realize high efficiency of 10 mA cm -2 in 1.0 M KOH with 0.33 M urea and delivered an even higher current density of 25 mA cm -2 at 1.46 V, which is smaller than that of the porous carbon and commercial Pt/C catalyst. Benefiting from theoretical calculations, Ni(III) active species and the porous carbon further enabled the electrocatalyst to effectively inhibit the "CO2 poisoning" of electrocatalysts, as well as ensuring its superior performance for urea oxidation.

Strategies for designing more efficient electrocatalysts towards the urea oxidation reaction

“…127 Therefore, it is expected that well-designed electrocatalysts with significantly lower reaction barriers for the desorption of the *COO intermediate from the catalytically active sites can possibly achieve better UOR performance. 143…”

Recent advances in the pre-oxidation process in electrocatalytic urea oxidation reactions

“…102 Similarly, satisfactory UOR activity with a low onset of 1.329 V vs. RHE can be achieved by growing the active NiO on an eggshell-like carbon skeleton, and a boosted pre-oxidation process with the in situ formation of NiOOH can be verified. 103 In addition, a bimetallic FeNi alloyed catalyst anchored on conductive CNTs derived from a metal-organic polymer was proposed by the Schechter group, which exhibits an enhanced pre-oxidation reaction as well as UOR activity compared to the FeNi alloy loaded on carbon, further proving the beneficial role of CNTs in promoting such electrochemical processes via regulating the charge transfer ability. 104 Conductive polymers could also be engaged in optimizing the charge transfer and facilitating the pre-oxidation reaction for the UOR.…”

Density Functional Theory Investigation of the NiO@Graphene Composite as a Urea Oxidation Catalyst in the Alkaline Electrolyte

“…In an earlier literature of UOR toward NiO and its derivatives, most of the theoretical studies have been performed by considering the adsorption/desorption of CO 2 in the gas–liquid interface, which matched well with the formed *COO species. 16 However, the competitive adsorption of urea and the hydroxyl group on the surface of the NiO-based electrocatalyst cannot be ignored before urea oxidation. Thus, to understand the competitive adsorption, both the adsorption energy of urea and the hydroxyl group were calculated.…”

“…Graphene was an alternative instead of porous carbon in our previous work with many advantages of high conductivity and stable support. 16 It is noted that graphene preferentially anchors NiO nanoparticles via electrostatic attraction due to its electronegativity. 23 Hence, we considered that the connection of NiO on the given graphene substrate was achieved by the Ni–O–C bond.…”

“… 16 NiO also possesses many merits, including easy-to-obtain, low-cost, and exchangeable valence states. 7 , 16 Meanwhile, graphene was employed as the alternative porous carbon for simulations. It is important to add theoretical simulation to understand the UOR process using different models, especially for the existence of a single-atom model due to attractive findings.…”