Final Report Summary - HYGENMEMS (Chip Integrated Hydrogen Generation-Storage-Power Micro System)
Project context and objectives
The main objective of the project was the career development of the researcher through acquiring additional knowledge, expertise and experimental skills in the modern, interdisciplinary research field of hydrogen energy-converting microsystems. The primary technical objective was exploring the possibilities and proof-of-concept for developing a chip-integrated hydrogen generator based on polymer electrolyte membrane water electrolysis, which was capable of a reverse operation as a hydrogen microfuel cell. The long-term goal was the technical realisation and fabrication of an integrated hydrogen generation-storage-power microsystem for autonomous energy supply of wireless electronic devices.
The competence of the host organisation and the researcher ideally complemented each other, building a strong basis for a successful realisation of these goals.
Work performed
The realisation of the personal development plan followed the principles of training-by-learning. The main activities included attending a variety of specialised lecture courses and practical training that aimed at increasing the competence of the researcher in the interdisciplinary field of microsystem technology. The specialised lectures covered various scientific topics, including surface and bulk analytical techniques, energy storage systems, sensors and actuators based on silicon microtechnology, etc. Another aspect of the training-by-learning approach focused on enhancing the competence and acquiring a systematic knowledge on project, quality and staff management, as well as improving social awareness and the capabilities to solve various teamwork issues and problems encountered in the research practice.
The training activities were dedicated mainly to experimental work carried out in the Clean Room Technology Center of IWE1. The researcher had access to the modern research facilities and support from highly competent scientists and engineers, received intensive training in all the technological processes (lithography, wet-bench processes, wet and dry etching, micro-electroplating, screen printing, micro assembling, etc.) and acquired the necessary practical skills to work independently with the available machines and the specific equipment (PVD machines, etchers, flip-chip bonders, die bonders, four-point resistance measurement station, etc.).
In parallel, the researcher made serious efforts to network in accordance with the European Commission's strategy for strengthening the European Research Area. She realised new professional contacts and collaborative links with leading scientists and research organisations in the field including the following:
- Juelich Research Center, Juelich; Fraunhofer Institute, Oldenburg; and Fuel Cell Technology, GmbH, Duisburg, Germany;
- Norwegian University of Science and Technology, Trondheim, Norway;
- Gebze Institute of Technology, GYTE, Turkey;
- Trinity College, University of Dublin, Ireland.
The scientific and technical realisation of the project included:
- development and testing of electrocatalysts for hydrogen energy conversion
The production of a single chip-integrated hydrogen microenergy system requires highly active, cost-efficient catalysts, deposited via preparation techniques that are compatible with the other microsystem technology processes. The method of magnetron sputtering was of particular interest. During the project, several mono and bimetallic systems (Pt, PtTi, PtIr) were deposited as thin sputtered films and investigated in detail. The performed parametric study was focused on the changes in the film morphology including its depth profile at varying dc-sputtering power, argon pressure and film thickness. The corresponding effects on the electrochemical active surface area and the catalytic efficiency toward the electrode reactions on the hydrogen and oxygen electrodes were followed. It was found that high sputtering pressure and low sputtering power are beneficial, ensuring a large active surface and increased catalytic activity. The performed morphological and electrochemical investigations revealed superior catalytic efficiency of the co-sputtered PtIr films with the best performance by the sample deposited at power ratio PPt:PIr = 100:30W containing 11 at. % Ir, which also had the most developed active surface. The observed effects were explained with the enhanced affinity of Ir to the formation of IrOHads surface coverage, electronic interaction between both metals and the established changes in the morphology of the bimetallic films.
- deposition of Pd films as hydrogen storage by dc magnetron sputtering
The hydrogen storage material of choice was palladium deposited by magnetron sputtering. In view of the device compatibility, it was very important to grow high-quality nano-structured Pd thin films on lattice non-matching substrates. The research allowed the establishment of an optimal sputter regime, resulting in the fabrication of fully reproducible Pd layers with a highly developed surface, moderate porosity and long-term mechanical stability, which was sustained during the whole range of film thicknesses tested (from 100 nm up to several ?m).
- formation of the polymer electrolyte membrane (PEM)
The PEM was fabricated by a spin coating of Nafion (20 wt. % solutions, ETEK) directly on the sputtered thin catalytic film. A set of coating parameters was found, allowing the fabrication of mechanically stable homogeneous PEM with controllable thickness and proton conductivity of around 5.10-3 S. cm-1 at ambient temperature and relative humidity, which is in accordance with the conductivity of the commercially available Nafion PEM. The PEM thickness was in the order 10-20 ?m and the voltage drop over the membrane at optimal electrolysis conditions was in the range of only a few mV.
- chip-integrated hydrogen generation-storage-power
All the components of the developed hydrogen energy-converting microsystem were built up on a single monocrystal Si (111) wafer using five different lithography masks. The technological scheme consisted of numbers of consecutive steps including metallisation, photolithography, wet chemical and dry plasma etching, magnetron sputtering, dicing and spin coating. The contact pads (Au) and the adhesive metal layers (Ti, Cr) were deposited by electron beam deposition/evaporation, while the catalytic films and the hydrogen storage material were fabricated by dc magnetron sputtering. The PEM was formed by spin coating. The HyGenMEMS performance characteristics were investigated on a single cell, using a self-designed laboratory testing device with possibilities to investigate the individual properties of the active and passive components, as well the functioning of the whole system both in an electrolyser (H2-charging) and in a fuel cell (discharging) mode.
The functioning of the HyGenMEMS in the charging regime was optimised in view of the electrode processes over-potential, efficiency, rate, duration, thickness and mechanical stability of the hydrogen storage layer. The best performance (10 mA.cm-2 at cell voltage of 1.74V energy efficiency 78-80 %) was achieved with a single cell having 500 nm thick Pd layer, 150 nm thick Pt as a hydrogen electrode catalyst, and a sputtered IrO2 as an anode (oxygen electrode) catalyst. The reverse FC operation of the chip-integrated microsystem showed worse characteristics compared to the electrolysis mode. The open circuit potential was around 0.5V and the maximum charge gained from the fuel cell after charging of the system, both to the maximum theoretical capacity of 0.67 C.cm-3 and to 0.167 C.cm-3 was 0.0034 C.cm-3 which is one fifth of its theoretical capacity. The maximum energy density of the HyGenMEMS single cell was 120 ?Wh.cm-2. The round trip efficiency of the system was around 40 %.
Main results
The project addressed a broad interdisciplinary research field. The researcher acquired expertise in the thin film processing and microsystem technology. The fulfilment of the technical part of the project resulted in a functioning prototype that proved the concept of the proposed reversible hydrogen microenergy system. Further research will be focused on development, design and integration of different numbers of HyGenMEMS single cells in stacks to fulfil specific energy needs and applications.
The main objective of the project was the career development of the researcher through acquiring additional knowledge, expertise and experimental skills in the modern, interdisciplinary research field of hydrogen energy-converting microsystems. The primary technical objective was exploring the possibilities and proof-of-concept for developing a chip-integrated hydrogen generator based on polymer electrolyte membrane water electrolysis, which was capable of a reverse operation as a hydrogen microfuel cell. The long-term goal was the technical realisation and fabrication of an integrated hydrogen generation-storage-power microsystem for autonomous energy supply of wireless electronic devices.
The competence of the host organisation and the researcher ideally complemented each other, building a strong basis for a successful realisation of these goals.
Work performed
The realisation of the personal development plan followed the principles of training-by-learning. The main activities included attending a variety of specialised lecture courses and practical training that aimed at increasing the competence of the researcher in the interdisciplinary field of microsystem technology. The specialised lectures covered various scientific topics, including surface and bulk analytical techniques, energy storage systems, sensors and actuators based on silicon microtechnology, etc. Another aspect of the training-by-learning approach focused on enhancing the competence and acquiring a systematic knowledge on project, quality and staff management, as well as improving social awareness and the capabilities to solve various teamwork issues and problems encountered in the research practice.
The training activities were dedicated mainly to experimental work carried out in the Clean Room Technology Center of IWE1. The researcher had access to the modern research facilities and support from highly competent scientists and engineers, received intensive training in all the technological processes (lithography, wet-bench processes, wet and dry etching, micro-electroplating, screen printing, micro assembling, etc.) and acquired the necessary practical skills to work independently with the available machines and the specific equipment (PVD machines, etchers, flip-chip bonders, die bonders, four-point resistance measurement station, etc.).
In parallel, the researcher made serious efforts to network in accordance with the European Commission's strategy for strengthening the European Research Area. She realised new professional contacts and collaborative links with leading scientists and research organisations in the field including the following:
- Juelich Research Center, Juelich; Fraunhofer Institute, Oldenburg; and Fuel Cell Technology, GmbH, Duisburg, Germany;
- Norwegian University of Science and Technology, Trondheim, Norway;
- Gebze Institute of Technology, GYTE, Turkey;
- Trinity College, University of Dublin, Ireland.
The scientific and technical realisation of the project included:
- development and testing of electrocatalysts for hydrogen energy conversion
The production of a single chip-integrated hydrogen microenergy system requires highly active, cost-efficient catalysts, deposited via preparation techniques that are compatible with the other microsystem technology processes. The method of magnetron sputtering was of particular interest. During the project, several mono and bimetallic systems (Pt, PtTi, PtIr) were deposited as thin sputtered films and investigated in detail. The performed parametric study was focused on the changes in the film morphology including its depth profile at varying dc-sputtering power, argon pressure and film thickness. The corresponding effects on the electrochemical active surface area and the catalytic efficiency toward the electrode reactions on the hydrogen and oxygen electrodes were followed. It was found that high sputtering pressure and low sputtering power are beneficial, ensuring a large active surface and increased catalytic activity. The performed morphological and electrochemical investigations revealed superior catalytic efficiency of the co-sputtered PtIr films with the best performance by the sample deposited at power ratio PPt:PIr = 100:30W containing 11 at. % Ir, which also had the most developed active surface. The observed effects were explained with the enhanced affinity of Ir to the formation of IrOHads surface coverage, electronic interaction between both metals and the established changes in the morphology of the bimetallic films.
- deposition of Pd films as hydrogen storage by dc magnetron sputtering
The hydrogen storage material of choice was palladium deposited by magnetron sputtering. In view of the device compatibility, it was very important to grow high-quality nano-structured Pd thin films on lattice non-matching substrates. The research allowed the establishment of an optimal sputter regime, resulting in the fabrication of fully reproducible Pd layers with a highly developed surface, moderate porosity and long-term mechanical stability, which was sustained during the whole range of film thicknesses tested (from 100 nm up to several ?m).
- formation of the polymer electrolyte membrane (PEM)
The PEM was fabricated by a spin coating of Nafion (20 wt. % solutions, ETEK) directly on the sputtered thin catalytic film. A set of coating parameters was found, allowing the fabrication of mechanically stable homogeneous PEM with controllable thickness and proton conductivity of around 5.10-3 S. cm-1 at ambient temperature and relative humidity, which is in accordance with the conductivity of the commercially available Nafion PEM. The PEM thickness was in the order 10-20 ?m and the voltage drop over the membrane at optimal electrolysis conditions was in the range of only a few mV.
- chip-integrated hydrogen generation-storage-power
All the components of the developed hydrogen energy-converting microsystem were built up on a single monocrystal Si (111) wafer using five different lithography masks. The technological scheme consisted of numbers of consecutive steps including metallisation, photolithography, wet chemical and dry plasma etching, magnetron sputtering, dicing and spin coating. The contact pads (Au) and the adhesive metal layers (Ti, Cr) were deposited by electron beam deposition/evaporation, while the catalytic films and the hydrogen storage material were fabricated by dc magnetron sputtering. The PEM was formed by spin coating. The HyGenMEMS performance characteristics were investigated on a single cell, using a self-designed laboratory testing device with possibilities to investigate the individual properties of the active and passive components, as well the functioning of the whole system both in an electrolyser (H2-charging) and in a fuel cell (discharging) mode.
The functioning of the HyGenMEMS in the charging regime was optimised in view of the electrode processes over-potential, efficiency, rate, duration, thickness and mechanical stability of the hydrogen storage layer. The best performance (10 mA.cm-2 at cell voltage of 1.74V energy efficiency 78-80 %) was achieved with a single cell having 500 nm thick Pd layer, 150 nm thick Pt as a hydrogen electrode catalyst, and a sputtered IrO2 as an anode (oxygen electrode) catalyst. The reverse FC operation of the chip-integrated microsystem showed worse characteristics compared to the electrolysis mode. The open circuit potential was around 0.5V and the maximum charge gained from the fuel cell after charging of the system, both to the maximum theoretical capacity of 0.67 C.cm-3 and to 0.167 C.cm-3 was 0.0034 C.cm-3 which is one fifth of its theoretical capacity. The maximum energy density of the HyGenMEMS single cell was 120 ?Wh.cm-2. The round trip efficiency of the system was around 40 %.
Main results
The project addressed a broad interdisciplinary research field. The researcher acquired expertise in the thin film processing and microsystem technology. The fulfilment of the technical part of the project resulted in a functioning prototype that proved the concept of the proposed reversible hydrogen microenergy system. Further research will be focused on development, design and integration of different numbers of HyGenMEMS single cells in stacks to fulfil specific energy needs and applications.
