High-Performance Hydroxide Exchange Membrane Fuel Cell Comprising an Atomic Layer-Deposited Silver Cathode

Atomic layer deposition (ALD) is emerging as an efficient tool for the precise manufacture of catalysts, owing to its sophisticated surface tailoring capabilities. To overcome the techno-economic limitations of fuel cell electric vehicles (FCEVs), which are considered suitable alternatives to battery electric vehicles (BEVs), the development of cost-efficient high-performance catalysts is essential. In this study, we successfully fabricated a Pt-free cathode for a hydroxide exchange membrane fuel cell (HEMFC) with excellent oxygen reduction activity under extremely low loading of Ag electrocatalysts using ALD. Microstructural analysis confirmed that the surface modification by ALD-Ag nanoparticles exhibited excellent step coverage characteristics on porous carbon nanotubes (CNTs). An HEMFC comprising a CNT cathode surface-decorated with ALD-Ag nanoparticles delivered a high peak power density of 2154 mW mgAg-1 in an alkaline environment at 65 °C. This study demonstrates the applicability of ALD for the manufacture of highly active low-cost electrocatalysts for high-performance HEMFCs.

Shape-tuned, surface-active and support-free silver oxygen reduction electrocatalyst enabled high performance fully non-PGM alkaline fuel cell

Exploring non-platinum group metal (n-PGM) based efficient oxygen reduction reaction (ORR) electro-catalysts is highly important for realizing advancement in sustainable next generation-alkaline anion exchange membrane fuel cells (AAEMFCs). Herein, we demonstrate a new “hierarchical shape tuning approach” for the synthesis of controlled sized and shaped non-PGM based Ag ORR electro-catalysts with surface active nano-islands. Hierarchical shapes ranging from spherical (S-AgNs), worm-in-sphere, sphere-in-worm and vermiform (worm-like) Ag nanostructures (V-AgNs) were obtained by precisely varying the ratios of capping agent to dual reducing agents in water at ambient conditions. Compared to S-AgNs, V-AgNs revealed a higher mass normalized ORR Tafel activity (0.303 A mg_Ag⁻¹ at 0.9 V), onset (1.06 V) and half wave (0.78 V) potentials and higher retention of limiting current density (>88%) after 5000 cycles in 0.5 M potassium hydroxide (KOH) solution attributable to their unique worm like morphology with surface active nano-islands and support free-nature enabled better catalyst utilization. In a fully “non-PGM AAEMFC” (n-PAAEMFC), V-AgNs exhibited the highest fuel cell activity of 115.6 mW cm⁻² and stable short-term durability (∼240 h) compared to S-AgNs (41.3 mW cm⁻²) and previously reported fully n-PAAEMFCs indicating their potential use in next-generation alkaline fuel cells.

A fully non-PGM alkaline membrane fuel cell with “highest fuel cell activity” was achieved using a hierarchically shape-tuned, small, surface-active, support-free, worm-shaped nano-structured silver oxygen reduction reaction electro-catalyst.

Oxygen reduction on silver catalysts electrodeposited on various nanocarbon supports

In this work, Ag particles were electrodeposited onto nitrogen-doped graphene oxide, graphene, multi-walled carbon nanotube (MWCNT), and Vulcan carbon XC-72R supports by varying the upper potential limit. The surface morphology of the resulting Ag-based catalysts was examined by scanning electron microscopy. The electrochemical oxygen reduction reaction (ORR) was tested in alkaline media employing the rotating disk electrode method. The variation of the upper potential limit influenced the size of silver nanoparticles and their number density on the substrate surface. All the Ag-based electrocatalysts studied in this work showed remarkable ORR activity in terms of half-wave potentials. The ORR results combined with hydrogen peroxide reduction results prove that all Ag catalysts tested are suitable for both reactions. Ag/NGO2 catalyst possesses the highest mass activity for ORR, which indicates a relationship between the Ag loading and electrocatalytic activity. The electroreduction of oxygen on all the electrodeposited silver catalysts follows a four-electron pathway in alkaline environment. These materials are promising alternatives for Pt/C catalyst to be used as alkaline membrane fuel cell cathodes.

The plasma-induced formation of silver nanocrystals in aqueous solution and their catalytic activity for oxygen reduction

Ag nanocrystals with different architectures are synthesized using a submerged plasma discharge without the involvement of any chemicals. The Ag architecture relies on the electron density in the plasma that could enable the Ag ions to be reduced instantaneously to generate a large number of small Ag nanoparticles. With a low electron density of 7.1 × 10^-22 m^-3, the Ag nanowires with a corrugated structure induced by twinning and stacking faults are formed along the entire longitudinal 〈111〉 direction. However, with a high electron density 13.7 × 10^-22 m^-3, the Ag nanodendrites are constructed with a defect-free structure. Due to the unique structure composed of twins and stacking faults, the Ag nanowires show a specific current density that is 2.7 times higher than the Ag nanodendrites towards the oxygen reduction reaction. This work not only suggests a synthetic route to the formation of nanowires with structural defects but also offers a rational design of electrocatalysts with enhanced catalytic activity.

Experimental investigation of upgrading of lignin-derived bio-oil component anisole catalyzed by carbon nanotube-supported molybdenum

Molybdenum supported on carbon nanotubes (CNTs) was synthesized and evaluated as a catalyst for the catalytic hydroprocessing of anisole.

Effect of Surface Ion Conductivity of Anion Exchange Membranes on Fuel Cell Performance

Anion conductivity at the surfaces of two anion-exchange membranes (AEMs), quaternized ammonium poly(arylene ether) multiblock copolymer (QPE-bl-3) and quaternized ammonium poly(arylene perfluoro-alkylene) copolymer (QPAF-1), synthesized by our group was investigated using current-sensing atomic force microscopy under purified air at various relative humidities. The anion-conducting spots were distributed inhomogeneously on the surface of QPE-bl-3, and the total areas of the anion-conducting spots and the current at each spot increased with humidity. The anion-conductive areas on QPAF-1 were found on the entire surface even at a low humidity. Distribution of the anion-conducting spots on the membrane was found to directly affect the performance of an AEM fuel cell.

Electrochemical-reduction-assisted assembly of ternary Ag nanoparticles/polyoxometalate/graphene nanohybrids and their activity in the electrocatalysis of oxygen reduction

Ternary Ag NPs@POM/rGO nanohybrids were synthesized by an electrochemical-reduction-assisted assembly method and had high electrocatalytic activity towards the oxygen reduction reaction.