Exploring highly efficient and low-cost electrocatalysts for the oxygen evolution reaction (OER) is very important for the development of renewable energy conversion and storage systems. Layered metal hydroxides have been studied with great interest owing to their high electrochemical activity and stability toward OER. Herein, we demonstrate an efficient approach to engineer the surface active sites in β-Co(OH)2 for enhanced electrocatalysis of OER. We employ a single-step bipolar electrochemical technique for the exfoliation of pristine β-Co(OH)2(Co(OH)2-Bulk) into thinner and smaller sheets. The as-synthesized Co(OH)2 nanostructures with improved active sites exhibit enhanced electrocatalytic activity toward OER with a very low overpotential of 390 mV at 10 mA cm–2 and a Tafel slope of 57 mV dec–1 in alkaline media. The results provide a promising lead for the development of efficient and economically viable electrode materials for oxygen evolution electrocatalysis.
The development of earth-abundant and highly efficient electrocatalysts for hydrogen evolution reaction (HER) in alkaline media is essential for practical alkaline water electrolysis. The possibility of tuning the electrocatalytic activity of alkaline HER electrocatalysts through various approaches, such as interfacial engineering or doping, has been recently explored. In this work, electrochemically exfoliated Co(OH)2 and chemically derived 1T-MoS2 nanostructures are electrostatically coupled to form a synergistic nanostructured two-dimensional heterostructure, which is shown to remarkably improve the HER activity in an alkaline medium. The Co(OH)2/1T-MoS2 heterostructure with an optimal 1:5 ratio (Co1Mo5) showed a low overpotential of 151 mV at a current density of 10 mA cm–2 and a Tafel slope of 94 mV dec–1 in alkaline media. The shift in the overpotential achieved for the heterostructure (>250 mV) compared to the individual MoS2 component is remarkably high, as per the earlier reports.
In this work, we demonstrate morphology‐controlled synthesis of flower‐like cobalt phosphide decorated on nitrogen doped reduced graphene oxide (NrGO), which act as bifunctional electrocatalysts toward both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The as‐synthesized CoP‐NrGO, formed via hydrothermal reaction followed by gas‐solid reaction, attains an OER current density of 10 mA cm−2 at an overpotential of 0.38 V, which is on par with that of its Co(OH)2‐NrGO counterpart and the benchmarked IrO2 catalyst. On the other hand, the conversion of Co(OH)2 to CoP is seen to improve its HER performance drastically. CoP‐NrGO reached a current density of 10 mA cm−2 at an overpotential of 0.184 V which is 0.204 V anodic to Co(OH)2‐NrGO. The improved performance could be attributed to reduced charge transfer resistance following the phosphidation process. From the comparison of the electrocatalytic performance of the catalysts, it can be inferred that phosphidation has a considerable effect only on the cathodic HER.
For the development of renewable energy conversion and storage systems, it is vital to investigate earth-abundant, noble-metal-free, and highly efficient electrocatalysts for the hydrogen evolution process (HER). Platinum and other precious metals-based electrocatalysts show better HER activity in acidic conditions than other electrocatalysts due to their fast kinetics and lower Tafel slope.[1] However, because they are rare and costly, they are challenging to deploy in practical applications. As a result, there has been an ongoing search for low-cost and earth-abundant materials that may be used as an efficient alternative for platinum-based electrocatalysts, with the goal of developing more cost-effective and inexpensive H2 manufacturing processes. The layered 2D nanomaterials have sparked a lot of scientific attention because of their tremendous potential for both fundamental and practical investigations. Natural minerals of the group V-VI (V = Bi, Sb; VI = S, Se) have exceptional optical and electrical characteristics.[2] Because of their availability, low cost, and tunable characteristics, antimony/bismuth-based chalcogenides are garnering a lot of attention as potential candidates as electrocatalysts for acidic HER. We have shown an efficient and straightforward approach for the electrochemical exfoliation of BiSbSe3 nanostructures from the ball-milled BiSbSe3 sample; the process parameters were adjusted in terms of time and applied voltage. Furthermore, a simple and straightforward electrophoretic deposition process was used to synthesize BiSbSe3 nanoparticles from exfoliated BiSbSe3 nanostructures. A DC voltage was supplied between the two inert electrodes in an aqueous electrolyte for the electrophoretic deposition of BiSbSe3 nanostructures directly onto a gold substrate. Charged particles or sheets suspended in the electrolyte are activated to migrate toward the electrode and deposit when a voltage is applied. The BiSbSe3 nanoparticles were deposited onto the positive electrode because the exfoliated BiSbSe3 nanostructures in water had a negative zeta potential. BiSbSe3 nanostructures prepared through electrochemical exfoliation method are electrophoretically deposited onto the gold substrate to obtain BiSbSe3 nanoparticles, were investigated as active electrocatalysts for HER in 0.5 M H2SO4 solution using a three-electrode set up. The optimized BiSbSe3 catalyst (10V10M-Au-7.5) is identified as highly active HER activity, having a low overpotential of 72 mV @ 10 mA cm−2 and a low Tafel slope of 31.6 mV dec-1, which far better than the antimony/bismuth chalcogenide system and very close to the state-of-the-art Pt/C catalyst. We demonstrate that the electrocatalytic HER activity is enhanced by highly active edge sites, large available surface active sites, defects created and partial oxidization of material during electrodeposition, and a synergistic effect between BiSbSe3 and the substrate. References [1] N.P. Dileep, T.V. Vineesh, P. V Sarma, M. V Chalil, C.S. Prasad, M.M. Shaijumon, Electrochemically Exfoliated β-Co(OH)2 Nanostructures for Enhanced Oxygen Evolution Electrocatalysis, ACS Appl. Energy Mater. 3 (2020) 1461–1467. https://doi.org/10.1021/acsaem.9b01901. [2] J. Wang, H. Yu, T. Wang, Y. Qiao, Y. Feng, K. Chen, Composition-Dependent Aspect Ratio and Photoconductivity of Ternary (BixSb1–x)2S3 Nanorods, ACS Appl. Mater. Interfaces. 10 (2018) 7334–7343. https://doi.org/10.1021/acsami.7b17253. Figure 1
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