Designing In Situ Grown Ternary Oxide/2D Ni-BDC MOF Nanocomposites on Nickel Foam as Efficient Electrocatalysts for Electrochemical Water Splitting

Abstract

The security of future energy, hydrogen, is subject to designing high-performance, stable, and low-cost electrocatalysts for hydrogen and oxygen evolution reactions (HERs and OERs), for the realization of efficient overall water splitting. Two-dimensional (2D) metal–organic frameworks (MOFs) introduce a large family of materials with versatile chemical and structural features for a variety of applications, such as supercapacitors, gas storage, and water splitting. Herein, a series of nanocomposites based on NCM/Ni-BDC@NF (NNi, CCo, M:FFe, CCu, and ZZn, BDC: benzene dicarboxylic acid, NF: nickel foam) were directly developed on NF using a facile yet scalable solvothermal method. After coupling, the electronic structure of metallic atoms was well-modulated. Based on the XPS results, for the NCF/Ni-BDC, cationic atoms shifted to higher oxidation states, favorable for the OER. Conversely, for the NCZ/Ni-BDC and NCC/Ni-BDC nanocomposites, cationic atoms shifted to lower oxidation states, advantageous for the HER. The as-prepared NCF/Ni-BDC demonstrated prominent OER performance, requiring only 1.35 and 1.68 V versus a reversible hydrogen electrode to afford 10 and 50 mA cm–2 current densities, respectively. On the cathodic side, NCZ/Ni-BDC exhibited the best HER activity with an overpotential of 170 and 350 mV to generate 10 and 50 mA cm–2, respectively, under 1.0 M KOH medium. In a two-electrode alkaline electrolyzer, the assembled NCZ/Ni-BDC (cathode) ∥ NCF/Ni-BDC (anode) couple demanded a cell voltage of only 1.58 V to produce 10 mA cm–2. The stability of NCF/Ni-BDC toward OER was also exemplary, experiencing a continuous operation at 10, 20, and 50 mA cm–2 for nearly 45 h. Surprisingly, the overpotential after OER stability at 50 mA cm–2 dropped drastically from 450 to 200 mV. Finally, the faradaic efficiencies for the overall water splitting revealed the respective values of 100 and 85% for the H2 and O2 production at a constant current density of 20 mA cm–2.

Tuning Electrochemical Hydrogen-Evolution Activity of CoMoO4 through Zn Incorporation

“…The HER kinetics, however, are facile irrespective of the specified overpotential of the catalyst. In this sense, it can be inferred that all reported catalysts have quite identical HER kinetics [9]. In addition, the kinetics of the HER in alkaline media can be realized by the mechanisms of adsorbing and desorbing hydrogen atoms or molecular hydrogen via either the Volmer-Heyrovsky or Volmer-Tafel pathways [56].…”

“…The lower BEs centered at 780.68 and 784.59 eV can be related to Co 2p 3/2 , while those located at higher BEs (796.71 and 800.20 eV) are correlated with Co 2p 1/2 . The Co 2p peak analysis shows that Co exists in oxidation states of 2+ and 3+ [9]. The high-resolution Mo 3d spectrum can be divided into two sets of doublets, which are ascribed to Mo 3d 3/2 at higher BEs (235.03 and 236.79 eV) and Mo 3d 5/2 at lower BEs (231.81 and 233.77 eV).…”

“…According to our previous study [9], 1 mg commercial 20% Pt/C was ultrasonically dispersed in a solution of pure ethanol (300 µL) and DI water (200 µL) for 30 min. Afterward, 10 µL Nafion solution was added and for another 30 min to gain a homogeneous ink solution.…”

“…A lot of recent publications have proved the excellent performance of TM-based compounds in water electrolysis. Among these compounds, transition metal oxides (TMOs), because of their low cost, rich redox properties, abundance, and durability under alkaline conditions, are one of the most promising candidates to consider [9,10].…”

Large-scale sonochemical fabrication of a Co3O4–CoFe2O4@MWCNT bifunctional electrocatalyst for enhanced OER/HER performances

“…31 Several methods have been suggested for fabricating mixed-phase binary and ternary nanocomposite (solid-state, sol-gel, hydrothermal, co-precipitation, etc.). [32][33][34][35] The benets of ultrasonic irradiation synthesis include large-scale synthesis, reduced reaction times, smaller product sizes, more precise control over synthesis conditions, less manufacturing costs, higher grade standards, less environmental effect, and so on. 36 Acoustic cavitation, the process by which bubbles form, expand, and then combust as a result of ultrasound irradiation, is responsible for most of the chemical effects of this type of irradiation.…”