HYDROGEN PRODUCTION
Hydrogen production by electrolysis (green hydrogen)
Through water electrolysis (electrochemical water splitting), pure H2 gas can be produced without emissions, with O2 formed as a by-product. The oxidation (anodic reaction) and reduction (cathodic reaction) occurring during water splitting take place in separate spaces, thus avoiding the formation of an explosive product mixture. The electrodes are separated by an electrolyte solution and a solid separator, or by a solid electrolyte replacing both, which ensures the ionic conduction required for the electrochemical processes.
Alkaline water electrolysis is the most mature technology and has been used on an industrial scale to produce H2 for the past 100 years. In this process, an alkaline electrolyte solution (typically KOH solution) is electrolysed between the cathode and the anode. A porous diaphragm is used to separate the two cell compartments and thus prevent O2 and H2 from mixing. To reduce the electrical resistance caused by the solution layer between the electrodes (and with it the cell voltage), electrolysis cells separated by a proton exchange membrane (PEM) were developed. In these, the anode and cathode are pressed directly against each other through a membrane (similar to fuel cells). Pure water is oxidised on the anode side, while at the cathode the H+ ions migrating through the membrane are reduced to hydrogen at the same rate.
Other, novel methods of hydrogen production.
A number of other, less mature technologies for producing green hydrogen are also available or under development. One example is direct water splitting using solar energy (e.g. by thermal, photo- or combined photo-thermal catalysis).
In addition to producing hydrogen, biological hydrogen production (e.g. with algae or bacteria) also enables the production of further CCU products (e.g. methane, alcohols). Beyond exploratory research, domestic applied research capacity in this field is available at the University of Szeged, the University of Pannonia, the Budapest University of Technology and Economics and within Power-to-Gas Hungary Kft.
Hydrogen can be used for energy generation in fuel cells, gas turbines and internal combustion engines. In gas turbines it is currently used only blended with natural gas, due to the high combustion chamber temperature. Fuel cells are the main conversion devices for both energy generation and transport use, so they are discussed in more detail below.
Balancing the energy system
The
energy produced by wind and solar fluctuates significantly,
and wind farms are often far from consumers. Therefore this
power must either be transmitted by cable to consumption
centres, or stored and then fed into the
energy system as needed. Hydrogen technology is one way to do this. Here,
electricity generated from renewable sources is used to power an electrolysis
process that splits water electrochemically
into hydrogen and oxygen – a form in which this
energy becomes storable and transportable. The hydrogen produced in this way
can then be converted back into electricity. This green hydrogen
serves to increase security of supply and the resilience of the
grid.
Ways of storing and using hydrogen
The
hydrogen produced in this way can be used directly. For example,
it can be converted into electricity using a fuel cell, or
used as a raw material in the chemical industry. The first question here is
how to make this hydrogen available for such purposes.