Novel Pt-poor catalysts for the electrocat. O2 reduction

The oxygen reduction reaction (ORR) is one of the most important electrocatalytic reactions due to its various applications, in particular in polymer electrolyte membrane (PEM) fuel cells, but also in oxygen sensors or, potentially, in metal air batteries. Until now, the best and most frequently used catalysts for the ORR are Pt-based materials, mainly carbon supported Pt or Pt-alloy nanoparticle catalysts. The high price for these materials is one of the main obstacles for the economically competitive introduction of PEM fuel cells. In the present project, we want to develop novel, Pt-poor or Pt-free oxide and oxycarbide/-nitride/oxycarbonitride early transition metal catalysts for the ORR, optimized with respect to activity, selectivity for H 2 O formation and corrosion stability under fuel cell relevant reaction conditions. This will be performed in a very systematic approach, via a deliberate tailoring of nanostructure, porosity and chemical composition of the catalyst and/or its support on the one hand correlated with its electrocatalytic performance on the other. This objective shall be reached by combining a synthetic sol-gel and template-directed approach towards mesoporous, high-surface area oxycarbonitride materials of titanium or tantalum of variable structure and composition with a very controlled in-situ approach of doping the material with carbon and nitrogen. The use of composite materials based on an infiltrated stable, highly porous carbon backbone exhibiting a multimodal pore system, as recently developed in the group of one of the applicants, will provide electrically conductive catalyst materials. The electrocatalytic reactions under up to fuel cell relevant reaction conditions will be tested with a wide range of sophisticated electrochemical, microscopic and (in situ) spectroscopy methodic approaches. In combination, these measurements will provide detailed information on the correlation between materials properties and catalytic performance as well as mechanistic information, and thus provide a basis for further target-oriented improvement of the catalyst materials.

The oxygen reduction reaction (ORR) is one of the most important electrocatalytic reactions due to its broad area of application, in particular in polymer electrolyte membrane (PEM) fuel cells, but also in oxygen sensors or, potentially, in metal air batteries. Until now, the best and most frequently used catalysts for the ORR are Pt-based materials, mainly carbon supported Pt or Pt-alloy nanoparticle catalysts. The high price for these materials is one of the main obstacles for the economically competitive introduction of PEM fuel cells. In the present project, we aimed at the development of novel, Pt-poor or Pt-free oxide and oxycarbide/-nitride/oxycarbonitride early transition metal (Ti, Ta) catalysts for the ORR, optimized with respect to activity, selectivity for H2O formation and corrosion stability under fuel cell relevant reaction conditions. This was performed in a very systematic approach, via a deliberate tailoring of nanostructure, porosity and chemical composition of the catalyst and/or its support on the one hand, and a systematic correlation with the electrocatalytic performance on the other.The project was divided into two work packages: In the first package (AG Hüsing, University of Salzburg) a synthetic approach to prepare mesoporous, high-surface area oxide materials of variable structure and composition combined with a very controlled approach of doping the material with carbon and nitrogen was developed. With titanium and tantalum (oxy)nitrides supported on spherical carbon particles a promising novel, electrocatalytically active composite material was synthesized. In the second work package (AG Behm, Ulm University) a wide range of sophisticated electrochemical, microscopic and (in situ) spectroscopy methodic approaches to study electrocatalytic reactions under up to fuel cell relevant reaction conditions was applied in a highly iterative and with the synthesis coupled way.In combination, these measurements have provided very detailed information on the correlation between materials properties and (electro)catalytic performance as well as mechanistic information, and thus provided a basis for further target-oriented improvement of the catalyst materials.