Trends in Catalysis and Catalyst Cost Effectiveness for N₂H₄Fuel Cells and Sensors: a Rotating Disk Electrode (RDE) Study

Abstract

Hydrazine (N2H4) is a promising high-power energy carrier for fuel cells, combining the energy density of methanol (MeOH) with the rapid oxidation kinetics of hydrogen (H2). N2H4 does not require expensive Pt group metals nor Au for low-potential (high voltage) oxidation, offering significantly lower fuel cell materials costs compared to H2, MeOH, ethanol (EtOH), and ammonia (NH3). In our study, we use rotating disk electrode (RDE) voltammetry to explore N2H4 oxidation at a wide variety of catalysts, including first-row transition metals (Co, Ni), coinage metals (Ag, Au) and Pt group metals (Ru, Rh, Pd, Ir, Pt). While several groups have focused on Co, Ni, or CoNi alloys, we find that other metals, including Ag, Ru, and Pd, offer much higher electron recovery and have more stable reactions, and still cost far less than Pt, Au, Rh, or Ir. We analyze our findings in terms of cost vs performance for the metals, developing a guide for the design of N2H4 fuel cell systems and sensors to suit various application spaces. The many metals studied also reveal an important trend for the theoretical understanding of catalysis: the onset and passivation of N2H4 oxidation in nearly every system were directly tied to the appearance or disappearance of specific metal surface states (e.g., hydrides and oxides). Indeed, metals with multiple surface states frequently showed multiple mechanisms for N2H4 oxidation, each with separate values for electron recovery. These observations provide support for the continued development of electrocatalytic theory in which different metal surface states are treated as independent materials with distinct reaction mechanisms.

A Multi‐Doped Electrocatalyst for Efficient Hydrazine Oxidation

“…[3] Theh ydrazine oxidation reaction (HzOR) is am ultielectron, multi-proton transformation. N 2 + 4H 2 O + 4e À .Direct hydrazine fuel cells were first proposed in the 1960s, [4] offering high theoretical electromotive force (1.56 V), zero carbon emissions,a nd easy fuel transportability.T he recent advances in alkaline membrane technology restarted the search for more efficient and selective electrocatalysts,m oving from scarce and costly elements (Pt, Pd, Au) [5,6] to earth-abundant materials (Fe, Ni, Co). N 2 + 4H 2 O + 4e À .Direct hydrazine fuel cells were first proposed in the 1960s, [4] offering high theoretical electromotive force (1.56 V), zero carbon emissions,a nd easy fuel transportability.T he recent advances in alkaline membrane technology restarted the search for more efficient and selective electrocatalysts,m oving from scarce and costly elements (Pt, Pd, Au) [5,6] to earth-abundant materials (Fe, Ni, Co).…”

A Multi‐Doped Electrocatalyst for Efficient Hydrazine Oxidation

“…Direct hydrazine fuel cells were first proposed in the 1960s, offering high theoretical electromotive force (1.56 V), zero carbon emissions, and easy fuel transportability. The recent advances in alkaline membrane technology restarted the search for more efficient and selective electrocatalysts, moving from scarce and costly elements (Pt, Pd, Au) to earth‐abundant materials (Fe, Ni, Co) . The latter, however, are easily covered by deactivating surface oxides.…”

Investigation of sodium borohydride and hydrazine oxidation on gold nanoparticles modified zinc–cobalt coating

“…The simple galvanic replacement of Zn by Pd or Au in the Ni-Zn coating enabled fabrication of the stable nanostructures of ternary or even quaternary catalysts like Ni/PdNi [39] or Cu/Ni/AuNi [40] with a reduced content of noble metal that seem to be promising ones for the direct borohydride fuel cells. A set of works based on non-precious Cocontaining [41][42][43][44][45][46][47][48][49], Ni, Ni binary and ternary alloy electrocatalysts [41,42,45,[49][50][51][52][53] for DHFCS have emerged either. Asazawa and co-workers presented a single-phase disordered noble metal-free Ni 60 Co 40 alloy electrocatalyst with a 6-fold increase in catalytic hydrazine hydrate oxidation activity over today's benchmark catalyst [46].…”