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  • Periodic Reporting for period 1 - ORRmetIR (Development and in situ Infrared study of Novel Strained Core-shell Electrocatalysts: Towards an Understanding of the Oxygen Reduction Mechanism)

ORRmetIR Report Summary

Project ID: 659306
Funded under: H2020-EU.1.3.2.

Periodic Reporting for period 1 - ORRmetIR (Development and in situ Infrared study of Novel Strained Core-shell Electrocatalysts: Towards an Understanding of the Oxygen Reduction Mechanism)

Reporting period: 2015-04-01 to 2017-03-31

Summary of the context and overall objectives of the project

The overall objectives: The project is directed towards understanding the reduction of oxygen gas to water on supported metal nanoparticles for fuel cell catalysis. This project uses absorption of infrared light to learn about intermediates in this reaction as it occurs on metal and novel core-shell metal nanoparticle materials.

Importance for society: Fuel cells are devices that convert a chemical (fuel) into electricity and are promising as part of a sustainable energy system for the future. Suitable fuels include hydrogen gas, ethanol and methanol, and use of these fuels is coupled to conversion of oxygen to water to produce electricity. The conversion of fuel and oxygen molecules occurs best on a metal surface called a catalyst where the metal helps to destabilise these molecules and break them apart. Good catalysts have been developed for the fuel reactions, but the oxygen conversion still presents a major limitation in development of fuel cell technologies. To date, platinum has emerged as the best catalyst for destabilising oxygen and turning it into water but platinum is even more expensive than gold and hence is undesirable for commercial use in large quantities. Moreover, pure platinum is still fairly slow at converting oxygen to water, so research is needed to find better catalysts for breaking down oxygen. This process which seems very simple actually follows a complex series of reaction steps which are not well understood, and learning about the complicated reaction mechanism is prerequisite to designing new well-defined core-shell catalysts. This project makes use of infrared light to study a range of known and new catalysts under real fuel cell conditions. Each molecule formed in the sequence of steps during conversion of oxygen to water absorbs a particular wavelength of infrared light and from this we can learn about which steps are involved on different metal catalyst surfaces.

Problem/issue being addressed: The target of this research was to develop a method which allows us to look at oxygen conversion in a functioning fuel cell to see how the catalyst really behaves, and to use this method to test and design new improved catalysts. We have tested and compared the overall activities and stabilities of these new well-defined catalysts during oxygen conversion to water and investigated the complicated reaction steps of conversion of oxygen to water with the help of infrared light. Thus, the research should take us a step closer to technologies for a sustainable energy future.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

Overview of the results:
(1) Core-shell carbon supported bimetallic Pt catalysts were synthesized using ordered mesoporous silica SBA-15 by reduction of metal precursors at high temperature under H2 gas.
(2) The synthesized catalysts were characterized using Synchrotron X-ray diffraction (XRD), High resolution transmission electron microscopy (HRTEM), Extended X-ray absorption fine structure (EXAFS), Inductively Coupled Plasma Mass Spectrometry (ICP-MS) and High sensitivity-low energy ion scattering (HS-LEIS).
(3) Electrochemical (rotating disk electrode; RDE) measurements were done to check the oxygen reduction activities and stabilities of unsupported and supported Pt (commercial and custom-made) and different metal ratios of bimetallic core-shell Pt-based catalysts under different reaction conditions. All the synthesized catalysts possess higher activities for oxygen reduction compared to the commercial Pt catalyst. These catalysts were also tested for methanol oxidation reaction and show better activities.
(4) Infrared set-ups was designed and implemented for in situ spectroelectrochemical experiments under fuel flow and temperature control. Potential dependent surface-adsorbed ORR intermediates (superoxide and peroxide) were detected at a carbon supported Pt catalyst following a 4 electron pathway.

Exploitation and dissemination of the results:
The fellow has attended the following conferences and gave oral presentations on the results from the project.
(1) Materials Research Society Fall Meeting, Boston, USA, 2015
(2) UK Catalysis, Loughborough, UK, 2015

The fellow is working on writing up further results from this project and is going to submit the following manuscript to high profile peer-reviewed journals:
(1) Detection of Adsorbed Superoxide on Pt electro-catalyst during Oxygen Reduction in acid media using in situ and operando Infrared spectroscopy; S. Nayak, I. J. McPherson, K. A. Vincent
(2) Core-shell bimetallic PtNi@C nanoparticles for oxygen reduction and methanol oxidation reactions; S. Nayak, E. Raine, F. Niu, A. Erbe, K. A. Vincent, E. Tsang

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

To date, Pt-based catalysts are still considered as the most active fuel cell catalysts. However, the high cost and scarcity of Pt makes it commercially unattractive and leaves room for development of cost effective fuel cell catalysts. Hence, efforts have been devoted to developing cheaper Pt-based bimetallic alloy catalysts. Unfortunately, this strategy presents a big challenge in synthesis as the nanoparticles required are thermodynamically unfavourable. Moreover, the synthesis of Pt-based core-shell structures in the sub-15 nm regime with a thin Pt atomic monolayer as a shell on a definite metal core poses difficulty and is scientifically challenging.

Secondly, commercialization of fuel cells is largely limited by the sluggish oxygen reduction reaction (ORR) kinetics causing high overpotential at the fuel cell cathode. The ORR is not only crucial for fuel cells but also for various other electrochemical processes such as metal-air batteries, metal corrosion and bio-catalysis. The mechanism of the multi-electron and multi-step ORR reaction, involving a set of reaction intermediates is still controversial and not well resolved. Poor understanding of the mechanism limits the development of efficient, inexpensive and improved fuel cell electrocatalysts, which is a major scientific concern. Traditional rotational ring disk electrode (RRDE) techniques discusses the ORR mechanism on the basis of various intermediate species that diffuse away from the electrode surface, without giving any structural information of adsorbed species. Infrared (IR) spectroscopy is a powerful technique which can be used in combination with electrochemical methods to give structural information about the ORR intermediates on the electrode surface.
Novel cost effective core-shell bimetallic Pt-based catalysts were developed and the ORR mechanism of these catalysts was investigated with the help of in situ infrared spectroscopy compared to the commercial Pt catalysts available in the market. They all showed higher activities compared to the commercial Pt catalyst and this information can be used to understand the ORR mechanism and design better energy efficient and stable fuel cell catalyst.

The development of lower-cost catalysts provides commercial exploitation opportunities as an alternative to current EU fuel cell and energy technologies. The results of the ‘ORRmetIR’ can serve as a basis for future alternate energy sources to minimise the use of fossil fuels. The output of ORRmetIR will underpin the advances needed to achieve the targets concerning clean and sustainable energy of Horizon 2020 Programme, and in turn will contribute to the European excellence in the competitive field of alternative energy sources.
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