Nanosized Proton Conductor Array with High Specific Surface Area Improves Fuel Cell Performance at Low Pt Loading

Abstract

The use of ordered catalyst layers, based on micro-/ nanostructured arrays such as the ordered Nafion array, has demonstrated great potential in reducing catalyst loading and improving fuel cell performance. However, the size (diameter) of the basic unit of the most existing ordered Nafion arrays, such as Nafion pillar or cone, is typically limited to micron or submicron sizes. Such small sizes only provide a limited number of proton transfer channels and a small specific area for catalyst loading. In this work, the ordered Nafion array with a pillar diameter of only 40 nm (D40) was successfully prepared through optimization of the Nafion solvent, thermal annealing temperature, and stripping mode from the anode alumina oxide (AAO) template. The density of D40 is 2.7 × 10 10 pillars/cm 2 , providing an abundance of proton transfer channels. Additionally, D40 has a specific area of up to 51.5 cm 2 /cm 2 , which offers a large area for catalyst loading. This, in turn, results in the interface between the catalyst layer and gas diffusion layer becoming closer. Consequently, the peak power densities of the fuel cells are 1.47 (array as anode) and 1.29 W/cm 2 (array as cathode), which are 3.3 and 2.9 times of that without array, respectively. The catalyst loading is significantly reduced to 17.6 (array as anode) and 61.0 μg/cm 2 (array as cathode). Thus, the nanosized Nafion array has been proven to have high fuel cell performance with low Pt catalyst loading. Moreover, this study also provides guidance for the design of a catalyst layer for water electrolysis and electrosynthesis.

In Situ Construction of a Nanostructured Ultrathin Catalyst Layer on Both Sides of a Membrane toward Fuel Cell Application

“…To reduce Pt loading and improve the activity and mass transfer of CL in CCMs, two major technical approaches have been widely employed. The first approach is to optimize the composition and structure of the conventional CLs by developing novel materials and/or optimizing the CCMs’ fabrication process. , The other approach is to construct the CCMs with nanostructured CLs, e.g., ordered or ultrathin CLs. − Middelman first proposed an ideal ordered CL composed of a vertically aligned Pt-nanoparticle-coated electron conductor uniformly covered by a thin ionomer film . Compared with conventional CLs, a structure-ordered CL is anticipated to intensify the active site exposure and mass transfer.…”

Proton Conductivity in a Metal–Organic Cube-Based Framework and Derived Hydrogel with Tubular Morphology

“…, as potential proton-conducting materials. − However, low chemical stability at relatively high temperature limits the widespread application of these materials in PEMFCs. Nafion, the ionomer, commercially used as a proton-exchange membrane in PEMFCs, is known to show appreciable proton conductivity at low temperature and high humidity. − However, its conductivity suffers a drastic downfall both with an increase in temperature and with a decrease in humidity. − Thus, development of new proton-conducting materials which operate at a wide temperature and humidity range, without compromising the chemical stability and mechanical strength, is of utmost importance for extracting the best performance of a PEMFC. − In this respect, porous materials such as metal–organic frameworks (MOFs) and porous organic materials (POMs) have recently emerged as an promising alternative. − Properties like high crystallinity, open framework architecture, and high structural stability not only make these materials better proton conductors but also provide ideal platforms for understanding the underneath mechanism of proton conductivity. − Few of the reported strategies to improve the conductivity of these materials involves increasing the concentration of proton carriers by tuning the framework or extraframework compositions and improving proton mobility by constructing materials with desired H-bonded networks. − However, the synthesis of these materials usually requires a greater degree of ligand deprotonation, which sometimes leads to a diminution of proton carrier concentration in the final porous architecture. As an alternative, researchers have recently demonstrated the synthesis of discrete metal–organic cages through partial deprotonation of ligands, which in turn resulted in much-improved proton conductivity of the porous architecture. , Interestingly, the finite structures of the metal–organic cages provide an opportunity to decorate their external surface with functional groups ( e.g.…”

In Situ-Grown Ultrathin Catalyst Layers for Improving both Proton Exchange Membrane Fuel Cell and Anion Exchange Membrane Fuel Cell Performances

“…However, when the above catalysts with high-performance intrinsic activity are incorporated into MEA for fuel cell applications, their actual output is far less than the predicted activity. , The critical reason is that the electrochemical tests are based on thinly coated catalysts at rotating disk electrodes, where some engineering-oriented problems (e.g., mass transfer, ion and electron transportations, etc.) do not exist. − Instead, in MEA fabrication, the powder catalysts are stacked in a disordered manner, resulting in increased ohmic and concentration losses. , To resolve this problem, an ultrathin catalyst layer (UTCL) is demonstrated by reducing the thickness of the catalyst layer. − The UTCL can significantly improve the catalyst layer mass transfer efficiency, , accelerate the electron transfer in the catalyst layer, , and improve the catalyst utilization, providing an effective way for solving the gas transport and electron conductivity problems for MEA. However, most of the reported UTCLs are typically fabricated by in situ growth on gas diffusion layers (GDLs).…”