Naturally Inspired Heme-Like Chemistries for the Oxygen Reduction Reaction: Going Beyond Platinum Group Metals in Proton Exchange Membrane Fuel Cell Catalysis

Authors

White R.J., White R.J.

Reference

Advances in Fabrication and Investigation of Nanomaterials for Industrial Applications, pp. 325-351, 2024

Description

In the context of the ongoing energy transition, electrochemical devices such as electrolysers and fuel cells (FC) will play a critical role in the implementation of a “Hydrogen Economy”. The ambition is to deliver the large-scale roll out of these devices that are capable of delivering ultrahigh energy/power densities in the case of FC using green Hydrogen (e.g. from renewables) to deliver electrical energy for specific applications (e.g. in msobility). The technology is well known for a number of decades, but there is an argument that at anticipated device production volumes (e.g. > Gigawatts per year), certain challenges remain to be addressed. The most common type of device architecture is the “Proton Exchange Membrane” FC (PEMFC), and here perhaps the most important challenge is the use of “Critical Raw Materials” (CRM), and specifically the use of “Platinum Group Metals” (PGM) in the fabrication of the active (e.g. catalytic) layers of the so-called “Membrane Electrode Assembly” (i.e. the key functional component of the fundamental FC unit cell). The sluggish reaction kinetics and large voltage hysteresis of the performance determining cathode reaction, the Oxygen Reduction Reaction (ORR), typically results in poor energy efficiency and low-capacity utilisation and thus dictates the high loading of high performance PGMs (e.g. >0.2 mg(Pt)/cm2 operating under the acidic conditions of the cathode). Owing to high(er) costs and resource scarcity of PGMs, their large-scale use (i.e. as Pt-based electrocatalysts in FCs) is expected to be limited, and as such a wide range of reports highlight potential substitutes. These have predominantly focused on reducing PGM loading and increasing intrinsic activity, with Metal-Nitrogen-Carbon (M-N-C) “Single Atom Catalysts” (SAC) being highlighted highly important alternative electrocatalysts. M-N-C catalysts present a number of potential advantages essentially arising from their active site chemistry, which is composed of a single atom (i.e. not conventional nanoparticles or clusters) and thus potentially can deliver 100%atomic utilisation. PGM substitution for M-N-C is thus attractive with respect to scale up and resource saving, particularly if these catalysts are based on more abundant elements (e.g. M = Fe). A number of other advantages can also arise in FC-related electrocatalysis, namely strong-metal interactions (e.g. increased stability and improve charge transfer), improved reaction selectivity (e.g. as consequence of repetitive active site electrochemistry/chemical states) and the delivery of high energy output from small catalyst amounts. However, reducing, for example, catalyst layer thickness (e.g. and therefore MEA thickness) and the consequences this has on device performance are still being explored. Thus, this chapter aims to provide an overview of the state of the art and latest R&D developments on M-N-C use in PEMFCs and specifically for the ORR reaction.

Link

doi:10.1007/978-3-031-42700-8_17