Functionalized Carbon Nanotubes with Ni(II) Bipyridine Complexes as Efficient Catalysts for the Alkaline Oxygen Evolution Reaction

Abstract

Among current technologies for hydrogen production as an environmentally friendly fuel, water splitting has attracted increasing attention. However, the efficiency of water electrolysis is severely limited by the large anodic overpotential and sluggish reaction rate of the oxygen evolution reaction (OER). To overcome this issue, the development of efficient electrocatalyst materials for the OER has drawn much attention. Here, we show that organometallic Ni­(II) complexes immobilized on the sidewalls of multiwalled carbon nanotubes (MWNTs) serve as highly active and stable OER electrocatalysts. This class of electrocatalyst materials is synthesized by covalent functionalization of the MWNTs with organometallic Ni bipyridine (bipy) complexes. The Ni-bipy-MWNT catalyst generates a current density of 10 mA cm–2 at overpotentials of 310 and 290 mV in 0.1 and 1 M NaOH, respectively, with a low Tafel slope of ∼35 mV dec–1, placing the material among the most active OER electrocatalysts reported so far. Different simple analysis techniques have been developed in this study to characterize such a class of electrocatalyst materials. Furthermore, density functional theory calculations have been performed to predict the stable coordination complexes of Ni before and after OER measurements.

An Insight on the Electrocatalytic Mechanistic Study of Pristine Ni MOF (BTC) in Alkaline Medium for Enhanced OER and UOR

“…It can be seen that Ni MOF shows 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 considerably higher catalytic activity than compared to NiO WCP and noble benchmark RuO 2 on CP substrate. [6] It indicates the pronounced and better catalytic activity of Ni MOF than NiO WCP and benchmark RuO 2 catalyst. [34] Figure 6b (catalytic current density at 300 and 400 mV of h) and Figure S6 in ESI (h required to produce 10 and 50 mA cm À2 current density) shows the specific catalytic activity of measured catalyst under identical conditions in this study; which show that Ni MOF possesses higher intrinsic catalytic activity towards OER than others in the exposed geometric area with same mass loading.…”

“…Wherein, Ni MOF appears less denser (see Figure S3 in ESI). [6,9,41,68,69] Meanwhile, the increased peak current density of Ni MOF redox couple compared to NiO WCP and RuO 2 indicates that Ni MOF possesses more Faradic active catalytic sites. In addition to it, the presence and distribution of Ni in the Ni MOF was analyzed using field emission scanning electron microscopy (FESEM) equipped with energy dispersive X-ray spectrum (EDX) detector and corresponding elemental mapping is shown in Figure S5 in ESI.…”

“…[3] It could be considered as a promising way to store renewable energy (solar and wind) in the grid scale in the form of H 2 and O 2 as water electrolysis require electrical energy and water source. [3,5,6,12] The well-known catalytic activity of noble catalysts Pt/C, IrO 2 and RuO 2 in cathode and anode respectively derive the WE at moderate overpotential (h; DE = E applied À1.23) of 400-500 mV at 10 mA cm À2 as per the recent benchmark which is equal to 10 % minimum solar to fuel conversion efficiency. [3,5,6,12] The well-known catalytic activity of noble catalysts Pt/C, IrO 2 and RuO 2 in cathode and anode respectively derive the WE at moderate overpotential (h; DE = E applied À1.23) of 400-500 mV at 10 mA cm À2 as per the recent benchmark which is equal to 10 % minimum solar to fuel conversion efficiency.…”

“…[1,2] Water electrolysis (WE) has been considered as a promising way to produce high pure H 2 than compared to earlier hydrocarbon and steam reformation process. [2,[4][5][6][7][8][9][10][11] In water electrolysis, anodic 4e À transfer oxygen evolution reaction (OER) is the limiting factor than compared to cathodic 2e À transfer hydrogen evolution reaction (HER). [2,[4][5][6][7][8][9][10][11] In water electrolysis, anodic 4e À transfer oxygen evolution reaction (OER) is the limiting factor than compared to cathodic 2e À transfer hydrogen evolution reaction (HER).…”

Convenient Immobilization of Cobalt Corroles on Carbon Nanotubes through Covalent Bonds for Electrocatalytic Hydrogen and Oxygen Evolution Reactions

“…The resulting CNTse ngineered with Co corroles were used as electrocatalysts for the hydrogen evolutionr eaction (HER) and the oxygen evolution reaction (OER) in aqueous solutions of pH 0, 7, and 14. [39][40][41][42][43] Despite these progresses,h owever, convenient methods for covalenti mmobilization under mild conditions are still needed.Carbon nanotubes (CNTs) are broadly used as supports for electrochemical applications because of their large surface areas and good electrical conductivities. This is likely because the large surface area and good electricalc onductivity of CNTsc an be well preserved during the amidationr eactionu nder mild conditions.…”