Electrocatalyst materials for low-temperature hydrogen fuel cells
Doctoral thesis, 2023
Fuel cells have emerged as an alternative to satisfy the need of energy systems with net-zero emissions. Although fuel cells date back to the 1800s, it is only during the last decades that research and development has enabled true commercialization. The growing interest in fuel cells implementation goes hand in hand with the decrease in green H2 production cost, which makes fuel cells a cornerstone in promising energy systems based on H2. It is crucial that the transport sector shifts towards inexpensive carbon-free fuel alternatives, which is possible with H2 owing to its high energy density. A broad implementation of fuel cells is, however, impeded by the high cost of fuel cell systems, which can be attributed to the Pt-based catalyst currently used in low-temperature hydrogen fuel cells. As Pt is a scarce expensive material, development of new efficient and inexpensive electrocatalysts is essential for large-scale fuel cells implementation.
Although many strategies have been explored to reduce the amount of Pt without compromising the power output and lifetime, electrocatalyst development is currently hindered by the lack of mechanistic understanding. In order to gain a better understanding of the mechanisms behind the electrochemical reactions in proton exchange membrane fuel cells (PEMFC) and anion exchange membrane fuel cells (AEMFC), this thesis delves into both the fabrication and the characterization of electrocatalysts. A versatile platform was established to study model system catalysts with the aim to test electrocatalytic materials and provide reliable comparisons, making their performance rationalizable in terms of geometric and electronic structure. Pt-rare earth metal (REM) alloys were studied with respect to both their activity and stability towards the oxygen reduction reaction (ORR) in PEMFCs. Measurements with different model systems indicated an overall increase in their specific activity, but it was found that the addition of REM could compromise their stability. Different Ag alloys were studied for the ORR in alkaline conditions. It was found that alloying could improve the binding energy of oxygenated species, which enhances their ORR activity. Hydrogen oxidation reaction (HOR) and ORR activity of PdNi annealed thin films in alkaline media were investigated to pinpoint the mechanism behind the increased activity. This provides insights to the fundamental principles that lead to a good catalyst efficiency, which was also tested with the addition of different ionomers. By providing additional insights on the mechanistic aspects of fuel cell reactions, the presented work takes a step in tailoring new electrocatalytic materials that could eventually outperform bare Pt in terms of both activity and stability while reducing the total fuel cell cost.
Although many strategies have been explored to reduce the amount of Pt without compromising the power output and lifetime, electrocatalyst development is currently hindered by the lack of mechanistic understanding. In order to gain a better understanding of the mechanisms behind the electrochemical reactions in proton exchange membrane fuel cells (PEMFC) and anion exchange membrane fuel cells (AEMFC), this thesis delves into both the fabrication and the characterization of electrocatalysts. A versatile platform was established to study model system catalysts with the aim to test electrocatalytic materials and provide reliable comparisons, making their performance rationalizable in terms of geometric and electronic structure. Pt-rare earth metal (REM) alloys were studied with respect to both their activity and stability towards the oxygen reduction reaction (ORR) in PEMFCs. Measurements with different model systems indicated an overall increase in their specific activity, but it was found that the addition of REM could compromise their stability. Different Ag alloys were studied for the ORR in alkaline conditions. It was found that alloying could improve the binding energy of oxygenated species, which enhances their ORR activity. Hydrogen oxidation reaction (HOR) and ORR activity of PdNi annealed thin films in alkaline media were investigated to pinpoint the mechanism behind the increased activity. This provides insights to the fundamental principles that lead to a good catalyst efficiency, which was also tested with the addition of different ionomers. By providing additional insights on the mechanistic aspects of fuel cell reactions, the presented work takes a step in tailoring new electrocatalytic materials that could eventually outperform bare Pt in terms of both activity and stability while reducing the total fuel cell cost.
Catalyst
Alloys.
Oxygen Reduction
Nanofabrication
Electrode
Fuel Cell
PEMFC
Hydrogen Oxidation
Model System
Thin Film
AEMFC
Pj-salen
Author
Gerard Montserrat Siso
Chalmers, Physics, Chemical Physics
With the urgent and evident need to address critical climate
challenges, the demand for a society with sustainable energy
systems has been brought to the fore. In this scenario, hydrogen
has emerged as a promising energy carrier since its use as a
fuel represents a ray of hope in the total decarbonization of the
energy sector. In order to truly achieve net-zero carbon
emissions, however, hydrogen needs to be produced from
renewable energy. Once produced, hydrogen can be used to
generate electrical power in a fuel cell, emitting only water and
heat as by-products. This rise hopes and expectations on this
energy conversion technology, which at times is unrealistically
positive. As an emerging technology, much remains to be
proven and the proper use of this technology in terms of suitable applications, integration with
society and extent of use is still under debate. Hence, if this entire energy cycle is meant to be
energetically profitable, there are a number of challenges that must be overcome.
Due to the large contribution of the transport sector to global carbon emissions, it is crucial that
this sector shifts towards inexpensive carbon-free fuel alternatives, which have provided the
impetus for low-temperature hydrogen fuel cell development and wide implementation.
However, commercialization of these sustainable energy systems is currently impeded by the
high cost of fuel cell components. The lack of inexpensive devices is greatly attributed to the
catalyst layers, in which scarce and costly materials are often used. Additionally, investigating
ready-to-use fuel cell catalytic materials is rather complicated due to the numerous components
and factors that contribute to the overall performance. Thus, in order to deconvolute the
interplay of such factors, well-defined electrocatalyst model systems have been used in this
work to provide insights on how to achieve high energy efficiency and durability in low-temperature
hydrogen fuel cells. Even though added values presented by fuel cell systems
introduced in niche markets already compensate for their initial cost, increased efficiency and
durability will result in a global broader use of this technology in the near term.
challenges, the demand for a society with sustainable energy
systems has been brought to the fore. In this scenario, hydrogen
has emerged as a promising energy carrier since its use as a
fuel represents a ray of hope in the total decarbonization of the
energy sector. In order to truly achieve net-zero carbon
emissions, however, hydrogen needs to be produced from
renewable energy. Once produced, hydrogen can be used to
generate electrical power in a fuel cell, emitting only water and
heat as by-products. This rise hopes and expectations on this
energy conversion technology, which at times is unrealistically
positive. As an emerging technology, much remains to be
proven and the proper use of this technology in terms of suitable applications, integration with
society and extent of use is still under debate. Hence, if this entire energy cycle is meant to be
energetically profitable, there are a number of challenges that must be overcome.
Due to the large contribution of the transport sector to global carbon emissions, it is crucial that
this sector shifts towards inexpensive carbon-free fuel alternatives, which have provided the
impetus for low-temperature hydrogen fuel cell development and wide implementation.
However, commercialization of these sustainable energy systems is currently impeded by the
high cost of fuel cell components. The lack of inexpensive devices is greatly attributed to the
catalyst layers, in which scarce and costly materials are often used. Additionally, investigating
ready-to-use fuel cell catalytic materials is rather complicated due to the numerous components
and factors that contribute to the overall performance. Thus, in order to deconvolute the
interplay of such factors, well-defined electrocatalyst model systems have been used in this
work to provide insights on how to achieve high energy efficiency and durability in low-temperature
hydrogen fuel cells. Even though added values presented by fuel cell systems
introduced in niche markets already compensate for their initial cost, increased efficiency and
durability will result in a global broader use of this technology in the near term.
Subject Categories
Physical Chemistry
Materials Chemistry
Other Physics Topics
Nano Technology
ISBN
978-91-7905-773-2
Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5239
Publisher
Chalmers
Pj-salen