Controllable and Scale-Up Synthesis of Nickel-Cobalt Boride@Borate/RGO Nanoflakes via Reactive Impingement Mixing: A High-Performance Supercapacitor Electrode and Electrocatalyst

Abstract

Large-scale synthesis of graphene-based nanomaterials in stirred tank reactor (STR) often results in serious agglomeration because of the poor control during micromixing process. In this work, reactive impingement mixing is conducted in a two-stage impinging jet microreactor (TS-IJMR) for the controllable and scale-up synthesis of nickel-cobalt boride@borate core-shell nanostructures on RGO flakes (NCBO/RGO). Benefiting from the good process control and improved micromixing efficiency of TS-IJMR, NCBO/RGO nanosheet provides a large BET surface area, abundant of suitable mesopores (2–5 nm), fast ion diffusion, and facile electron transfer within the whole electrode. Therefore, NCBO/RGO electrode exhibits a high specific capacitance of 2383 F g−1 at 1 A g−1, and still retains 1650 F g−1 when the current density is increased to 20 A g−1, much higher than those of nickel boride@borate/RGO (NBO/RGO) and cobalt boride@borate/RGO (CBO/RGO) synthesized in TS-IJMR, as well as NCBO/RGO-S synthesized in STR. In addition, an asymmetric supercapacitor (NCBO/RGO//AC) is constructed with NCBO/RGO and activated carbon (AC), which displays a high energy density of 53.3 W h kg−1 and long cyclic lifespan with 91.8% capacitance retention after 5000 charge-discharge cycles. Finally, NCBO/RGO is used as OER electrocatalyst to possess a low overpotential of 309 mV at a current density of 10 mA cm−2 and delivers a good long-term durability for 10 h. This study opens up the potential of controllable and scale-up synthesis of NCBO/RGO nanosheets for high-performance supercapacitor electrode materials and OER catalysts.

Robust and Promising Electrocatalytic Oxygen Evolution Reaction by Activated Cu–Co–B Amorphous Nanosheets

“…Even though the amorphous phase is obtained in powder XRD measurements and lattice fringes were not seen under high magnification TEM imaging (Figures a and S1), we performed ultrahigh-resolution TEM imaging using the field emission cathode (Figure d–f). The CuCo 2 B nanosheets showed two types of lattice spacing (0.21 and 0.16 nm), which can be corroborated to the cobalt boron phase. , The Fourier transformation infrared spectroscopy (FTIR) measurement ensured the formation of the Cu–Co–B phase (Figures g and S4). In the enlarged FTIR spectra, the peaks at around 450–500 cm –1 are attributed to the M–B stretching vibration frequency, which ratifies the formation of a novel CuCo 2 B alloy .…”

Easy and Support-Free Synthesis of Bimetallic Borates for Boosting the Oxygen Evolution Reaction

“…A comparison of the electrocatalytic activity of M@CoB i for the OER with the most promising MB i s from the recent literature is presented in Table S1 and Figure f, demonstrating the significance of the effects produced by the introduction of Ni into CoB i . Figure f shows that better OER catalytic activity than those obtained in this work can only be achieved by using CoB i s with conductive substrates such as Ni foam, CC, reduced graphene oxide (RGO), and graphene (G), which significantly increase the cost and production time of these catalysts. Another strategy to achieve this state-of-the-art-like performance is obtained by doping CoB i s with Ru atoms .…”

“…28,29 However, the preparation of these materials is costly and requires tedious synthesis routes. Moreover, TMB i s used as catalysts for the OER are usually prepared on conductive materials, such as Ni foam, 30,31 Ti mesh, 24 carbon cloth (CC), 26 or self-supported graphene, 32 in order to improve their performance. These supports increase the cost and difficulty of the process, making the implementation of TMB i s as OER anodes more difficult.…”

“…Cobalt borates (CoB i s), the most studied TMB i s, are believed to catalyze the hydroxylation step in the water splitting mechanism, making them very promising as electrocatalysts for the OER. − In this regard, other TMB i s, such as nickel borates, have been studied as efficient electrocatalysts for the OER. , However, the preparation of these materials is costly and requires tedious synthesis routes. Moreover, TMB i s used as catalysts for the OER are usually prepared on conductive materials, such as Ni foam, , Ti mesh, carbon cloth (CC), or self-supported graphene, in order to improve their performance. These supports increase the cost and difficulty of the process, making the implementation of TMB i s as OER anodes more difficult.…”

“…These supports increase the cost and difficulty of the process, making the implementation of TMB i s as OER anodes more difficult. Subsequently, codoped CoB i s, such as nickel-cobalt ,, or iron-cobalt borates, can modify the oxidation state of Co atoms in pristine CoB i , inducing and providing new active sites for electrocatalytic reactions, appearing as advanced catalysts for the OER. However, to the best of our knowledge, no detailed analysis of the effect of different codoped agents in CoB i s has been reported.…”