Mechanism Study of Hydrazine Electrooxidation Reaction on Nickel Oxide Surface in Alkaline Electrolyte by In Situ XAFS

Abstract

This study introduces a new insight on the mechanism of selective electrooxidation of hydrazine in alkaline media. The catalytic process takes place on nickel oxide surface of a Ni oxide nano-particle decorated carbon support (NiO/C). The catalyst was synthesized by wet impregnation and a liquid reduction procedure followed by thermal annealing. In-situ X-ray absorption fine structure (XAFS) spectroscopy was used to investigate the reaction mechanism for hydrazine electrooxidation on NiO surface. The spectra of X-ray absorption near-edge structure (XANES) of Ni K-edge indicated that adsorption of OH − on Ni site during the hydrazine electrooxidation reaction. Density functional theory (DFT) calculations were used to elucidate and suggest the mechanism of the electrooxidation and specifically propose the localization of electron density from OH − to 3d orbital of Ni in NiO. It is found that the accessibility of Ni atomic sites in NiO structure is critical for hydrazine electrooxidation. Based on this study, we propose a possible reaction mechanism for selective hydrazine electrooxidation to water and nitrogen taking place on NiO surface as it is applicable to direct hydrazine alkaline membrane fuel cells. Diversification of fuel is important to enhance the versatility of fuel cells as viable power devices for the next generation. Liquid fuel such as methanol, ethanol, borohydride, formic acid, 2-propanol, dimethyl ether and hydrazine are liquid chemical substances that include hydrogen and are considered an energy source in which hydrogen is an electron carrier. The advantages of liquid fuels include, but are not limited to high energy density and ease of handling at both the energy supply and demand sides. In the case of liquid fuel, simple/existing infrastructure, such as conventional petrol stations, is sufficient as for fuel supply, and while the geographic and temporal gap between energy supply and receipt are being filled this would allow to concentrate and leveraging off energy contribution to the expansion of and market penetration of fuel cell technology.Direct hydrazine hydrate fuel cells (DHFCs) utilizing an anion exchange membrane have recently attracted attention as a clean power device. Hydrazine contains no carbon and excretes harmless nitrogen and water by theoretical electroreaction and non-platinum group metal (PGM) catalysts such as Fe, Co, and Ni. These catalysts have been demonstrated for both the anode and cathode electrodes as shown Fig. 1a. The fuel cell vehicle equipped with no PGM as catalysts was demonstrated at SPring-8 in 2013. We believe this demonstration of DHFCs as a power device contributes to the reduction of CO 2 emissions and begins to address the fossil fuel resource problem. If zero CO 2 emission fuel cell vehicles (FCVs), are to be deployed using carbon-free liquid fuel, the emissions of CO 2 would be associated only with the liquid fuel manufacturing facility side and the measures of reduction of CO 2 emission by the transportation sector are would be supported by the depl...

Structure of Active Sites of Fe-N-C Nano-Catalysts for Alkaline Exchange Membrane Fuel Cells

“…To reveal the mechanism of HO 2 − generation, Fe-N-C ORR electrocatalysts synthesized with variation of several parameters were analyzed by synchrotron X-ray radiation to build structure-to-properties correlations on the basis of our previous works [30,31,32,33]. The structure of electrocatalysts, which is associated with Fe-N x motive and the presence of Fe metallic particle showed the clear difference in the variation of composition, processing and treatment conditions of SSM.…”

Advances in Nickel Nanoparticle Synthesis via Oleylamine Route

“…The similarity of the spectra of NiNPs and Ni film indicates the formation of pure Ni(0). The absence of an intense white line at around 8345 eV in the XANES spectrum of NiNPs and bulk Ni verifies the valence differences of nickel in the nanoparticles compared to the bivalent state in NiO and Ni(acac) 2 .This proves the formation of pure non-oxidized NiNPs[35,36].…”

Ultra‐sensitive Amperometric Hydrazine Sensing via Dimethyl Glyoxomat Derived NiO Nanostructures

“…Based on the behavior of hydrazine at NiO‐GCE and in view of literature report , we propose the following electrocatalytic mechanism for oxidation of hydrazine which results in facilitated electron transfer (Scheme ):…”

“…In other words the presence of OH − and NiO surface both are essential for adsorption and subsequent desortion in order to result in rapid transfer of OH − for elecrocatalytic oxidation of hydrazine. Similar discussion is also described elsewhere .…”