Performance and Stability of Aemion and Aemion+ Membranes in Zero-Gap CO2 Electrolyzers with Mild Anolyte Solutions.

The dependence of performance and stability of a zero-gap CO2 electrolyzer on the properties of the anion exchange membrane (AEM) is examined. This work firstly assesses the influence of the anolyte when using an Aemion membrane and then shows that when using 10 mM KHCO3 , a CO2 electrolyzer using a next-generation Aemion+ membrane can achieve lower cell voltages and longer lifetimes due to increased water permeation. The impact of lower permselectivity of Aemion+ on water transport is also discussed. Using Aemion+, a cell voltage of 3.17 V at 200 mA cm-2 is achieved at room temperature, with a faradaic efficiency of >90 %. Stable CO2 electrolysis at 100 mA cm-2 is demonstrated for 100 h, but with reduced lifetime at 300 mA cm-2 . However, the lifetime of the cell at high current densities is shown to be increased by improving water transport characteristics of the AEM and reducing dimensional swelling, as well as by improving cathode design to reduce localized dehydration of the membrane.

Comparative Study of PtNi Nanowire Array Electrodes toward Oxygen Reduction Reaction by Half-Cell Measurement and PEMFC Test.

A clear understanding of catalytic activity enhancement mechanisms in fuel cell operation is necessary for a full degree translation of the latest generation of non-Pt/C fuel cell electrocatalysts into high-performance electrodes in proton-exchange membrane fuel cells (PEMFCs). In this work, PtNi nanowire (NW) array gas diffusion electrodes (GDEs) are fabricated from Pt NW arrays with Ni impregnation. A 2.84-fold improvement in the oxygen reduction reaction catalytic activity is observed for the PtNi NW array GDE (cf. the Pt NW array GDE) using half-cell GDE measurement in a 0.1 M HClO4 aqueous electrolyte at 25 °C, in comparison to only a 1.07-fold power density recorded in the PEMFC single-cell test. An ionomer is shown to significantly increase the electrochemically active surface area of the GDEs, but the PtNi NW array GDE suffers from Ni ion contamination at a high temperature, contributing to decreased catalytic activities and limited improvement in operating PEMFCs.

Annealing Behaviour of Pt and PtNi Nanowires for Proton Exchange Membrane Fuel Cells.

PtNi alloy and hybrid structures have shown impressive catalytic activities toward the cathodic oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). However, such promise does not often translate into improved electrode performances in PEMFC devices. In this contribution, a Ni impregnation and subsequent annealing method, translatable to vertically aligned nanowire gas diffusion electrodes (GDEs), is shown in thin-film rotating disk electrode measurements (TFRDE) to enhance the ORR mass activity of Pt nanowires (NWs) supported on carbon (Pt NWs/C) by around 1.78 times. Physical characterisation results indicate that this improvement can be attributed to a combination of Ni alloying of the nanowires with retention of the morphology, while demonstrating that Ni can also help improve the thermal stability of Pt NWs. These catalysts are then tested in single PEMFCs. Lower power performances are achieved for PtNi NWs/C than Pt NWs/C. A further investigation confirms the different surface behaviour between Pt NWs and PtNi NWs when in contact with electrolyte ionomer in the electrodes in PEMFC operation. Indications are that this interaction exacerbates reactant mass transport limitations not seen with TFRDE measurements.