Noble Metal-Free Hydrazine Fuel Cell Catalysts: EPOC Effect in Competing Chemical and Electrochemical Reaction Pathways

Abstract

We report the discovery of a highly active Ni-Co alloy electrocatalyst for the oxidation of hydrazine (N(2)H(4)) and provide evidence for competing electrochemical (faradaic) and chemical (nonfaradaic) reaction pathways. The electrochemical conversion of hydrazine on catalytic surfaces in fuel cells is of great scientific and technological interest, because it offers multiple redox states, complex reaction pathways, and significantly more favorable energy and power densities compared to hydrogen fuel. Structure-reactivity relations of a Ni(60)Co(40) alloy electrocatalyst are presented with a 6-fold increase in catalytic N(2)H(4) oxidation activity over today's benchmark catalysts. We further study the mechanistic pathways of the catalytic N(2)H(4) conversion as function of the applied electrode potential using differentially pumped electrochemical mass spectrometry (DEMS). At positive overpotentials, N(2)H(4) is electrooxidized into nitrogen consuming hydroxide ions, which is the fuel cell-relevant faradaic reaction pathway. In parallel, N(2)H(4) decomposes chemically into molecular nitrogen and hydrogen over a broad range of electrode potentials. The electroless chemical decomposition rate was controlled by the electrode potential, suggesting a rare example of a liquid-phase electrochemical promotion effect of a chemical catalytic reaction ("EPOC"). The coexisting electrocatalytic (faradaic) and heterogeneous catalytic (electroless, nonfaradaic) reaction pathways have important implications for the efficiency of hydrazine fuel cells.

Single Crystalline Ultrathin Nickel–Cobalt Alloy Nanosheets Array for Direct Hydrazine Fuel Cells

“…As shown in Figure 3 A, generally the ultrathin Ni x Co 1− x ‐ANSAs exhibit a lower onset potential ( E on ) and faster current density increase as Co content increased, but the trend terminated as x = 0.5. Under optimized Ni:Co ratio, Ni 0.6 Co 0.4 ‐ANSA shows the highest HzOR activity, which is in accord with the previous report 11. Figure 3B shows that the E on of ultrathin Ni 0.6 Co 0.4 ‐ANSA was 30 mV lower than that of Ni‐NSA, demonstrating a higher intrinsic activity toward hydrazine oxidation.…”

“…Such overwhelming electrocatalytic performance of the ultrathin Ni 0.6 Co 0.4 ‐ANSA is ascribed to the extremely high intrinsic activity toward hydrazine oxidation,11, 22 and the ultrahigh surface areas and a plethora of unsaturated atoms (i.e., surface atoms, step/corner atoms) induced by the ultrathin 2D nanostructures. Those dangling atoms could act as highly active electrocatalytic sites.…”

A new near-infrared ratiometric fluorescent probe for hydrazine

“…[1][2][3] Due to its ammable and detonable characteristics, hydrazine is oen applied in rocketpropulsion systems and missile systems. 4 However, hydrazine is a class of highly toxic and pollutant compound, which can potentially lead to serious environmental contamination during its manufacture, use, transport and disposal.…”

High-performance polypyrrole functionalized PtPd electrocatalysts based on PtPd/PPy/PtPd three-layered nanotube arrays for the electrooxidation of small organic molecules

“…[1][2][3][4][5] However, several critical issues must be solved before Pt-based electrocatalysts can be commercialized. For example, the electrocatalytic reaction is kinetically limited, the low CO poisoning tolerance causes severe durability of catalyst, and the scale of Pt catalysts leads to high cost.…”