Periodic Reporting for period 1 - Thin-CATALYzER (Nanostructured anode catalyst layer for oxygen evolution reaction based on a novel thin-film architecture)
Reporting period: 2020-09-01 to 2022-08-31
The development of secure, clean and efficient energy represents a fundamental societal challenge for Europe. Enormous technological challenges are awaiting not just in relation to the substitution of carbon-based fuels and systems but also to a rational utilization of the power generated by renewable sources (e.g. sun, wind), which are abundant but intermittent in nature, therefore requiring the development of an efficient energy storage back-up system. In such a scenario, power-to-gas technology, which relies on the production of a synthetic fuel by using electric power, is a very powerful approach as it is able to fulfill a number of functions. They include electrical energy storage in the form of hydrogen or its derivatives, production of carbon-free fuel for industry and mobility, transportation of energy via a gas distribution grid and supply of stand-alone systems.
In the power-to-gas process, water electrolysis, by which electricity is used to split water into molecular hydrogen and oxygen, plays a central role. Since the commercially available alkaline water electrolysis cells (which are based on anion exchange membranes) are insufficient for responding to the future demands in power-to-gas-systems owing to their low current density, the low purity of the produced H2 and the low dynamics, alternative technologies have recently come to the fore. Among these, Proton Exchange Membranes Electrolysis Cells (PEMECs), whose core is a solid polymer electrolyte, exhibit a number of highly competitive technological advantages. Owing to the high power density, the high gas purity, the rapid system response, the large dynamic range of operation and the compact design, PEMECs are ideal for operating in synergy with intermittent and variable power sources such as renewables.
PEMEC systems are a novel technology which will greatly benefit from innovation deriving from R&D activities. The project Thin-CATALYzER (thin-film based CATalyst LaYer for oxygen Evolution Reaction) promotes the practical implementation of PEMECs by developing a novel thin-film based platform for fundamental investigations and for the fabrication of a technologically relevant catalyst layer, which serves both to gain new understanding on the fundamental mechanisms of water electrolysis and for tackling some of the main current limitations of state-of-the-art PEMEC systems.
In the power-to-gas process, water electrolysis, by which electricity is used to split water into molecular hydrogen and oxygen, plays a central role. Since the commercially available alkaline water electrolysis cells (which are based on anion exchange membranes) are insufficient for responding to the future demands in power-to-gas-systems owing to their low current density, the low purity of the produced H2 and the low dynamics, alternative technologies have recently come to the fore. Among these, Proton Exchange Membranes Electrolysis Cells (PEMECs), whose core is a solid polymer electrolyte, exhibit a number of highly competitive technological advantages. Owing to the high power density, the high gas purity, the rapid system response, the large dynamic range of operation and the compact design, PEMECs are ideal for operating in synergy with intermittent and variable power sources such as renewables.
PEMEC systems are a novel technology which will greatly benefit from innovation deriving from R&D activities. The project Thin-CATALYzER (thin-film based CATalyst LaYer for oxygen Evolution Reaction) promotes the practical implementation of PEMECs by developing a novel thin-film based platform for fundamental investigations and for the fabrication of a technologically relevant catalyst layer, which serves both to gain new understanding on the fundamental mechanisms of water electrolysis and for tackling some of the main current limitations of state-of-the-art PEMEC systems.
During the project, a new catalyst layer for PEMEC has been fabricated. It is a core-shell structure based on carbon fibers, coated by an ultrathin ceramic layer. This structure ensures high electrical conductivity and protection against corrosion. A fine dispersion of Iridium nanoparticles provides catalytic activity. The specific work has been the following:
1) Fabrication and electrochemical characterization of a TiO2-based model system. Specific work has been carried out in order to optimize the morphological and electrical properties of the TiO2 support layer. A comparative analysis between different thin-film fabrication techniques has been carried out, considering physical methods (pulsed laser deposition (PLD) and atomic layer deposition (ALD). ALD has been eventually chosen, owing to the unique capability to obtain conformal layers with minimized thickness. Different post-processes (H2 reduction and nitridation) have been tested in order to achieve the target in-plane conductivity. The optimized layers present a metallic behavior with high conductivity in a thickness range from 10-40 nm. Taking advantage of the specific knowledge of the host institution National Institute of Chemistry (NIC) in the fabrication of noble metal nanoparticles, a process for Ir nanoparticles fabrication on top of the TiO2 support has been implemented. The process leads to a finely dispersed distribution of NPs.
2) Realization of a highly porous anode catalyst layer.
Upon project revision, a highly potentially alternative to the initially proposed support structure (commercial TiO2 grids) has been adopted. The support consists of C nanofibers coated by TiO2. The backbone C structure, which has been introduced in the project thanks to a collaboration with the Catalonia Institute for Energy Research (IREC), offers unique advantages of open mesoporosity and high electrical conductivity. The processing of C fiber fabrication is carried out by electrospinning, a scalable technology with potential applicability at the industrial level. Conformal TiO2 coating and Ir NPs functionalization have been achieved according to the processes optimized for the model system (cf. objective 1). The so-obtained structure has been tested electrochemically for OER initial performance and long term stability. The layer presents high activity. Post-mortem characterization points towards coating layer oxidation as the main source of layer degradation.
1) Fabrication and electrochemical characterization of a TiO2-based model system. Specific work has been carried out in order to optimize the morphological and electrical properties of the TiO2 support layer. A comparative analysis between different thin-film fabrication techniques has been carried out, considering physical methods (pulsed laser deposition (PLD) and atomic layer deposition (ALD). ALD has been eventually chosen, owing to the unique capability to obtain conformal layers with minimized thickness. Different post-processes (H2 reduction and nitridation) have been tested in order to achieve the target in-plane conductivity. The optimized layers present a metallic behavior with high conductivity in a thickness range from 10-40 nm. Taking advantage of the specific knowledge of the host institution National Institute of Chemistry (NIC) in the fabrication of noble metal nanoparticles, a process for Ir nanoparticles fabrication on top of the TiO2 support has been implemented. The process leads to a finely dispersed distribution of NPs.
2) Realization of a highly porous anode catalyst layer.
Upon project revision, a highly potentially alternative to the initially proposed support structure (commercial TiO2 grids) has been adopted. The support consists of C nanofibers coated by TiO2. The backbone C structure, which has been introduced in the project thanks to a collaboration with the Catalonia Institute for Energy Research (IREC), offers unique advantages of open mesoporosity and high electrical conductivity. The processing of C fiber fabrication is carried out by electrospinning, a scalable technology with potential applicability at the industrial level. Conformal TiO2 coating and Ir NPs functionalization have been achieved according to the processes optimized for the model system (cf. objective 1). The so-obtained structure has been tested electrochemically for OER initial performance and long term stability. The layer presents high activity. Post-mortem characterization points towards coating layer oxidation as the main source of layer degradation.
The project has validated a new architecture for efficient electrocatalytic processes. The architecture presents high performance and minimized use of critical raw materials. It can be applied in a straightforward way in low-temeprature electrochemical devices such as polimeric fuel cells and electrolyzers and is based on scalable manufacturing techniques. It promises therefore to have a positive impact on the penetration of low-impact technologies for green hydrogen production and utilization, supporting the achievemnt of a net-zero economy by the European Union.