GREEN ENERGY VIA ELECTROCHEMICAL PROCESSES (GEEP)

This PhD three years project is centred on the world energy policy that would like to achieve the carbon neutrality by reducing the use of fossil fuel to produce energy and substitute it with renewable sources of energy. First, the energy policy of European Union and United State are presented to understand which are the two most important occidental energetic policy. And it is understood that both two main actors have the policy to reduce greenhouse gas emission and achieve the net zero emission in 2050. Different technologies permit to achieve the net zero emission depending on the sector in which the fossil fuel need to be replaced from the renewable energy. The main thing is how it is possible to store the energy coming from renewable sources. Because for all the renewable sources of energy, apart from the nuclear energy, the main problem is connected to their nature. They are not constant in time, and they are not equally distributed on the territory. But the energy coming from fossil fuel is disponible every time and everywhere there is an engine and a tank of fuel. In the last year some different technologies are investigated and enveloped to store energy. These technologies could store energy via mechanical processes or via electrical processes or via biological processes or via electrochemical processes or via chemical processes and all these technologies could be efficiently used to decarbonize one ore different energy sectors. In this PhD project titled “Green Energy via Electrochemical Processes” are investigated obviously different electrochemical processes to store energy. It is decided to study the electrochemical processes that permit to split the water into H2 using renewable source of energy. And from these large number of electrochemical processes are selected the polymer exchange membrane processes the more stable Proton Exchange Membrane Water Electrolyzer (PEMWE) and the promising Anion Exchange Membrane Water Electrolyser (AEMWE). It is decided to investigate the green hydrogen production in correlation to the European union energy policy that has the scope to decarbonize, the industrial production, mainly steel, cement and chemicals industry and heavy and long transport made by route or ship, the air transport and the heating sectors by the production of green hydrogen. The main part of that project is centred on the AEMWE, that is one of the most promising technologies for the future implementation of green hydrogen production. It is decided to focus the attention on the cathodic side of the electrolysers, because the Hydrogen Evolution Reaction (HER) in alkaline environment is one of the key points of that technologies because to have a good efficiency it is necessary to use a large quantity of noble metal catalysts, mainly Pt based catalysts. And it is an important voice of the CAPEX cost of these devices. Then it is investigated a new composite electrocatalyst material, made by an oxophilic component in strict interaction of a noble metal because some scientific paper evidenced that the presence of an oxophilic material in synergistic interaction with the noble metal rise the catalyst mass activity for the HER in alkaline environment. And connected to the necessity to reduce the amount of noble metal used to produce an AEMWE the Ion Beam Sputtering Deposition (IBSD) technique is selected to be investigated as synthetic method that permit to synthetized and deposited a thin composite catalysts layer on a generic substrate. This technique is selected because is easily scalable and produce a compact, reproducible thin durable thin layer start from a metal composite target. Zr has been selected as oxophilic element and as noble metal Pd and Pt. It is verified the synergistic interaction between the two catalysts component in the obtained thin layer electrode on FTO substrate and it is decided to verify which is the best thickness between 200, 100, 50 and 25 nm of the composite catalysts layer made by IBSD on FTO. Many samples are made by IBSD on FTO to be characterized electrochemically and physically and it is evidenced that all the sample made by IBSD show a synergistic interaction between the two composite catalyst components. The IBSD permits to obtain reproducible thin layer samples in term of composition, roughness and electrochemical properties. And for both the Pt@ZrO2 and Pd@ZrO2 on FTO substrate the best thin layer thickness is 50 nm in term of HER. Finally, to demonstrate that IBSD is a promising technique for Membrane Electrode Assembly (MEA) manufacturing it is made a 50 nm Pt@ZrO2 catalysts layer on a commercial Anion Exchange Membrane with an active area of 50 cm2. And this MEA is assembled into the industrial partner (Claind) AEMWE device to be characterized as electrochemical hydrogen generator. The results obtained are promising for possible future implementation after an optimization of the production processes. In parallel, due to Claind exigence, is made the envelopment of the manual hot pressing spray deposition process to produce a Membrane Electrode Assembly for the PEMWE Claind device. The aim of that part of the project is addressed to solve a Claind production problem centred on the final purity of the H2 that need to be highly pure because Claind H2 generators are used for analytical applications. Another parallel work is made in correlation to the PEMWE topic. Electrodeposited Iridium oxide film is characterized by Electrochemical Impedance Spectroscopy, to obtain the proton diffusion coefficient at different overpotential near to the OER. With the aim of verify which is the difference in term of proton diffusion coefficient between a highly hydrated Iridium oxide films and a sputtered or low hydrated films. Because the proton diffusion in the catalyst films influenced the Oxygen Evolution Reaction that in acidic environments it the most sluggish reaction. Due to that EIS permit to characterize a deposited IrO2 film and by know the thickness of the deposited film obtain the proton diffusion coefficient that is a key point to evaluate this type of catalysts for the OER in acidic environment. And respect to other spectroscopic investigation is more rapid, less expensive and easier to make. As consequence of the large bibliographic research on the topics connected to the green H2 production and conversion in alkaline environment a review is made on the topic of Oxygen Reduction Reaction (ORR) Pt based nanostructured electrocatalysts material. This is connected to the exigence of some application to have a device that can work as H2 generators to store energy and burn the produced H2 to make energy when energy is required. And in the case of a device in which the reduction occurs always in the same chamber in both situations the HER and the ORR electrocatalysts need to be the same. And finally, another parallel work is made on an experimental setup that use EIS instrument to generate a AC current signal and by measure the potential difference permit to evaluate semiconductors conductive type. This method is enveloped due to the large experience made on EIS instrumentation during this three years PhD project. This is a good method for an easy and rapid evaluation of different semiconductor.