Development of Hydrogen-Oxygen Fuel Cells Based on Anion-Exchange Electrolytes and Catalysts with Reduced Platinum Content

Studies have been carried out to optimize the composition, formation technique and test conditions of membrane electrode assemblies (MEA) of hydrogen-oxygen anion-exchange membranes fuel cells (AEMFC), based on Fumatech anion-exchange membranes. A non-platinum catalytic system based on nitrogen-doped CNT (CNT_N) was used in the cathode. PtMo/CNT_N catalysts with a reduced content of platinum (10-12 wt.% Pt) were compared with 10 and 60 wt.% Pt/CNT_N at the anode. According to the results of studies under model conditions, it was found that the PtMo/CNT_N catalyst is significantly superior to the 10 and 60 wt.% Pt/CNT_N catalyst in terms of activity in the hydrogen oxidation reaction based on the mass of platinum. The addition of the Fumion ionomer results in minor changes in the electrochemically active surface area and activity in the hydrogen oxidation reaction for each of the catalysts. In this case, the introduction of ionomer-Fumion leads to a partial blocking of the outer surface and the micropore surface, which is most pronounced in the case of the 60Pt/CNT_N catalyst. This effect can cause a decrease in the characteristics of MEA AEMFC upon passing from 10PtMo/CNT_N to 60Pt/CNT_N in the anode active layer. The maximum power density of the optimized MEA based on 10PtMo/CNT_N was 62 mW cm^-2, which exceeds the literature data obtained under similar test conditions for MEA based on platinum cathode and anode catalysts and Fumatech membranes (41 mW cm^-2). A new result of this work is the study of the effect of the ionomer (Fumion) on the characteristics of catalysts. It is shown that the synthesized 10PtMo/CNT_N catalyst retains high activity in the presence of an ionomer under model conditions and in the MEA based on it.

PtM/CNT (M = Mo, Ni, CoCr) Electrocatalysts with Reduced Platinum Content for Anodic Hydrogen Oxidation and Cathodic Oxygen Reduction in Alkaline Electrolytes

Bimetallic catalysts containing platinum and transition metals (PtM, M = Mo, Ni, CoCr) were synthesized on carbon nanotubes (CNTs) functionalized in an alkaline medium. Their platinum content is 10–15% by mass. PtM/CNTNaOH are active in both the hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (ORR) in alkaline electrolytes. Although catalysts based on a single transition metal are inactive in the HOR, their activity in the cathode process of ORR increases relative to CNTNaOH. When using the rotating ring-disk electrode method for ORR, PtM/CNT showed a high selectivity in reducing oxygen directly to water. In HOR, the PtM/CNT catalyst had an activity comparable to that of a commercial monoplatinum catalyst. The results obtained show that it is possible to use the PtM/CNT catalyst in an alkaline fuel cell both as an anode and as a cathode.

Model Study of CNT-Based PEMFCs’ Electrocatalytic Layers

One of the most important problems in the development of proton-exchange membrane fuel cells (PEMFCs) is the selection of an efficient support material to serve as the electrocatalyst, which can ensure PEMFCs’ durability at low active metal loading, with minimal changes in the electrochemical surface and conductivity during long-term operations. Carbon nanostructures are now widely used in PEMFCs as such support materials, including carbon nanotubes (CNTs). In order to estimate the effect of the geometric parameters of a CNT-based support on the resulting size distribution of platinum nanoparticles for given synthesis conditions, in this work, we propose a semi-empirical model that assumes a random uniform distribution of platinum particles over the CNT surface. Based on the obtained distribution, the electrochemically active surface area (EASA) of the electrocatalyst is calculated and further used to evaluate the performance of the catalytic layer (CL) in the PEMFC. The applicability of the proposed model for calculating the parameters of CNT-based CLs and the output electrochemical characteristics of PEMFCs is shown.

Nanocomposite Cathode Catalysts Containing Platinum Deposited on Carbon Nanotubes Modified by O, N, and P Atoms

Platinum deposited on dispersed materials has so far been the most demanded catalyst for creating cathodes for a wide range of electrochemical power sources. This paper sets out to investigate the effect of carbon nanotube (CNT) modification by O, N, and P atoms on the structural, electrocatalytic, and corrosion properties of the as-synthesized monoplatinum catalysts. The investigated Pt/CNTmod catalysts showed an increased electrochemically active platinum surface area and electrical conductivity, as well as an increased catalytic activity in the oxygen reduction reaction (ORR) in alkaline electrolytes. The improved characteristics of Pt/CNT catalysts are explained by alterations in the composition and number of groups, which are formed on the CNT surface, and their electronic structure. By the sum of the main characteristics, Pt/CNTHNO3+N and Pt/CNTHNO3+NP are the most promising catalysts for use as cathode materials in alkaline media.