Transition Metal Carbides and Nitrides as Electrode Materials for Low Temperature Fuel Cells

Abstract

Transition metal carbides (TMCs) and transition metal nitrides (TMNs) have attracted attention as promising electrocatalysts that could replace noble metals of high price and limited supply. Relative to parent metals, TMC and TMN behave like noble metals for electrochemical reactions such as oxidation of hydrogen, CO and alcohols, and reduction of oxygen. When TMC and TMN are combined with other metals, the electrocatalytic synergy is often observed in electrochemical reactions. Thus, combinations with a minute amount of Pt or even non-Pt metals give performance comparable to heavily loaded Pt-based electrocatalysts for low temperature fuel cells. It appears that TMC based electrocatalysts are more active as anode catalysts for oxidation of fuels, whereas TMN based catalysts are more active for cathode catalysts for oxygen reduction and more stable.

Earth‐Abundant Nanomaterials for Oxygen Reduction

“…[58] They are more difficult to etch at higher overpotential where most transition-metals tend to dissolve.N itrogen can be easily inserted in the interstitial sites of early transition metals with negligible change to the crystal, which significantly improve the d-band structure.T hese changes can narrow the Fermi-level gap of transition metals compared with noble metals,l eading to improved catalytic performance. [59] Furthermore,b onding of nitrogen with less electronegative elements (e.g.t ransition metals) leads to charge transfer in the resulting nitrides.T his charge transfer activates the surface by producing acidic/basic sites for sorption of oxygenated species and modifying the dband electron density,r esulting in improvement of the catalytic response. [60] Several single-metal (TiN,C oN x , Mo x N y ,V N x ,W N x ,A lN) [61][62][63][64][65][66] and multi-metallic (Co-Mo, Co-W) [67,68] nitrides were designed and synthesized to improve the ORR performance.T he potential electrocatalytic application of MN x as an electrode in redox systems was identified for the first time by using TiNa samodel in the basic electrolyte.…”

Platinfreie Nanomaterialien für die Sauerstoffreduktion

“…Diese Veränderungen kçnnen die Lücke am Fermi-Niveau der Übergangsmetalle verglichen mit Edelmetallen verengen, was zu der besseren katalytischen Leistung führt. [59] Darüber hinaus führt die Bindung von Stickstoff an weniger elektronegative Elemente (z. B. Übergangsmetalle) zu einem Ladungstransfer in die resultierenden Nitride.D ieser Ladungstransfer aktiviert die Oberfläche,i ndem er saure/basische Zentren für die Sorption der oxygenierten Spezies schafft und die Elektronendichte im d-Band modifiziert, was zu einer Verbesserung der katalytischen Aktivität führt.…”

Durable Transition‐Metal‐Carbide‐Supported Pt–Ru Anodes for Direct Methanol Fuel Cells

“…The carbides of Groups IV-VI, in particular, exhibit catalytic properties akin to platinum-group metals. Indeed, there have been several attempts to utilize tungsten carbide (WC) as an electro-catalyst because of its platinum-like catalytic behavior, its stability in acid solutions at anodic potentials, and its resistance to CO poisoning [12]. But when used as an anodic material in a DMFC, pristine WC exhibits low electrocatalytic activity albeit its resistance to CO poisoning [13].…”