Enhancing the Stability and Performance of Mo-Doped Titanium Suboxide Fuel Cell Catalyst Supports

Abstract

Polymer electrolyte membrane fuel cells (PEMFCs) are a near-commercial clean energy technology with potential application in automotive and station power systems. However, the high cost of Pt catalyst and long-term durability of electrode materials still represents barriers towards that hinder market gains for the technology. The catalyst support material greatly influences electrocatalytic activity and durability of the catalytic Pt nanoparticles. Carbon black has been the primary catalyst support in fuel cells over the last 30 years due to its high surface area and electrical conductivity. However, carbon corrosion occurs readily during start-up/shutdown conditions. Therefore, more advanced support materials are need in order to overcome these problems.Metal oxides supports have improved corrosion resistance over carbon black supports, but they typically lack the required electrical conductivity for high performance. Titanium suboxides, specifically those doped with Mo (TOM) and other metals, have been shown to have acceptable electronic conductivity and strong affinity for Pt nanoparticles, to enhance their activity and stability in fuel cells. However, doping with only Mo still creates materials with a sizable band bandgap of 2.6 eV. Furthermore, the long term stability of the Mo dopant is a potential concern.Our group has taken a two-pronged approach to improving TOM materials. The first approach has been to add a second dopant. Specifically, we have a new material doped with both Mo and Si, Ti3O5-Mo-Si (hereafter referred to as TOMS) support. Remarkably, this support has a band gap of only 0.31 eV, approaching the conductivity of a metal. Furthermore, the TOMS material are highly durable and corrosion resistant, showing no signs of dopant loss under extremely corrosive conditions.Our second approach to improving TOM has been to convert it into a nanotube structure (TNTS-Mo) and from there covalently attach a monolayer of a nitrogen-rich terpyridine (tpy) ligand to the surface of the support (hereafter referred to as TPY/TNTS-Mo). The tpy ligand serves as a protective barrier that stabilizes the TNTS-Mo support. Furthermore, the nitrogen groups also have an electronic interaction with Pt catalyst nanoparticles that enhances their stability under harsh operating conditions.In this presentation, we will give an overview of support modification methods as well as detailed discussion of catalyst durability. Figure 1