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

Abstract

Hydrogen production plays a major role in technologies for renewable energy storage. Water and urea electrolysis (WE, UE) are promising processes in this regard. The oxygen evolution reaction (OER) and urea oxidation reaction (UOR), respectively, are limiting the efficiency of the overall process. As catalysts for these reactions, metal-organic frameworks (MOF) have gained increasing attention due to their combinations and co-existence of metal and organic moiety properties. Here, we investigated the catalytic behavior of Ni MOF (1,3,5-Benzenetricarboxylic acid (BTC)) towards OER and UOR in alkaline medium on carbon paper (CP) as a support. The Ni MOF exhibits 346 mV overpotential (h) at a current density of 10 mA cm À2 , 79.03 A g À1 specific-mass activity at 400 mV of h than compared to wet chemically prepared (WCP) NiO and RuO 2 for OER in 1 M KOH. Meanwhile, % 230 mV of h at 10 mA cm À2 current density with appreciable stability for 12 hours for Ni MOF in 30 % KOH was also observed. For UOR in UE, Ni MOF shows an onset potential of 1.34 V vs. RHE and 63.15 mA cm À2 current density at 1.5 V vs RHE in 1 M KOH in the presence of 1 M urea. The observed results of OER and UOR catalytic behavior are better than wet chemically prepared (WCP) NiO and noble benchmark RuO 2 catalyst under identical conditions. The results suggested that the MOF plays a major role in enhancing the catalytic activity by the facile formation of Ni(OH) 2 /NiOOH, stability and electronic properties due to their porous and interconnected structure.

Electrochemical Cathodic Treatment of Mild Steel as a Host for Ni(OH)2 Catalyst for Oxygen Evolution Reaction in Alkaline Media

“…[24,25] In the case of Ni(OH) 2 deposited MS and C MS Ni(OH) 2 after OER cyclic sweep, peaks at 471 and 557 cm À 1 indicate the NiÀ O vibrations of Ni(OH) 2 /NiOOH. [10,26,27] In accordance with the surface morphology analysis, Raman spectroscopy measurements suggest the formation of Fe(OH) 2 /Fe(OOH) surface layer on the MS by the cathodic treatment in the alkaline solution (1 M KOH) and it is another evidence for the existence of electrodeposited Ni (OH) 2 on the MS and C MS Ni(OH) 2 after OER cyclic sweep. It may due to the interaction of surface modified Fe(OH) 2 /FeOOH and Ni(OH) 2 with each other.…”

“…Meanwhile, the observed redox peak potential shift in C MS Ni(OH) 2 as compared to MS Ni(OH) 2 is due to the interaction of Fe(OH) 2 /FeOOH with the Ni(OH) 2 . The higher observed redox peak current density and area under the redox peaks (directly proportional to the Faradic electrochemical active sites) for C MS Ni(OH) 2 shows its wealthy catalytic activity towards OER . To support the Faradaic electrochemical active sites, electrochemical active surface area (ECSA) was estimated through double layer capacitance ( C dl ; Δ j =| j a – j c |) measurements in the non‐Faradic region.…”

“…The higher observed redox peak current density and area under the redox peaks (directly proportional to the Faradic electrochemical active sites) for C MS Ni(OH) 2 shows its wealthy catalytic activity towards OER. [9,10] To support the Faradaic electrochemical active sites, electrochemical active surface area (ECSA) was estimated through double layer capacitance (C dl ; Δj = j j a -j c j) measurements in the non-Faradic region. C dl is directly proportional to the ECSA of catalysts.…”

“…[16][17][18] To further emphasize the catalytic characteristics, EIS study was utilized to describe the solution induced resistance (R s ) at the electrode/catalysts/electrolyte interface and charge transfer resistance (R ct ) in the OER condition. [1,8,10,[37][38][39] Figure 7(a and b) depicts the EIS Nyquist and Bode plots measured at 300 mV of η in 1 M KOH. It shows that OER by the catalysts comprises of R s and R ct with the Warburg diffusion of OH À ions towards the electrode surface and away of O 2 .…”

“…In this regard, Ni, Fe and Co containing materials in the form of alloys, oxides, hydroxides, layered hydroxides, spinels, pyrites, nitrides, carbide, metal organic frame works and it derivatives are employed as electrocatalysts. [4,6,[10][11][12] Electrocatalysts are adhered on supporting current collectors using binders (Nafion, PTFE, PVDF). However, binders hinder the electrical conductivity to certain extent and result in resistance towards the charge transfer of electrochemical reaction, block the electrochemical active sites which impede the interaction of electrochemical active sites with the electrolyte and other reactive species.…”