Iryna V. Zenyuk

Platinum group metal-free NiMo hydrogen oxidation catalysts: high performance and durability in alkaline exchange membrane fuel cells

We introduce a new platinum group metal-free (PGM-free) hydrogen oxidation electrocatalyst with superior performance in anodes of alkaline exchange membrane fuel cells (AEMFCs). A carbon-supported bimetallic nickel–molybdenum catalyst was synthesized by thermal reduction of transition metal precursors on the surface of a carbon support (KetjenBlack 600J). The mass-weighted activity of 4.5 A gMe−1 determined in a liquid electrolyte 0.1 M NaOH using a rotating disk electrode (RDE) technique is comparable to the value reported for Pd/C with a comparable particle size under similar conditions. This NiMo/KB catalyst was integrated in a membrane electrode assembly (MEA) using an alkaline exchange membrane and ionomer. Single AEMFC tests performed in a H2/O2 configuration resulted in a record power density output of 120 mW cm−2 at 0.5 V, the MEA was found to be durable under the conditions of potential hold of 0.7 V for 115 h. For the first time, operando X-ray computed tomography (CT) experiments were performed demonstrating liquid water formation at the PGM-free anode during cell operation, and in situ ambient pressure X-ray photoelectron spectroscopy (APXPS) and X-ray absorption spectroscopy (APXAS) were used to study the role of molybdenum in hydrogen adsorption.

Nickel–copper supported on a carbon black hydrogen oxidation catalyst integrated into an anion-exchange membrane fuel cell

This work introduces the first practical platinum group metal-free (PGM-free) electrocatalyst for the hydrogen oxidation reaction (HOR) in alkaline membrane fuel cells (AMFCs), based on nickel-rich Ni95Cu5-alloy nanoparticles supported on Ketjenblack (KB) family carbon blacks. The catalyst synthesis is scalable and results in an expected true alloy of NiCu, which is thoroughly characterized by XRD, microscopy and XPS. The reactivity of the catalyst towards the HOR is studied by cyclic voltammetry and explained in view of its composition and structure. This catalyst showed the highest specific activity compared to previously reported NiCu electrocatalysts and was successfully integrated into an AMFC membrane electrode assembly (MEA) using a commercially available state-of-the-art membrane and an ionomer. Single MEA fuel cell tests have demonstrated a power density of 350 mW cm−2 at 80 °C, which sets a technical record for a PGM-free anode in realistic operating conditions. The MEA with the NiCu/KB anode catalyst layer was evaluated by in situ nano- and in operando micro-X-ray computed tomography (CT) and the results suggest that the nickel state in NiCu is hydrophobic in nature, where the NiCu surface may be isostructural with β-Ni(OH)2. The hydrophobic nature of the electrocatalyst allows for improved water distribution in the MEA and overall fuel cell as observed by in operando micro-X-ray CT.