Electrical Connection: Hydrogen, the power source of the future

As Australia, and the world moves  further unto the renewable space, Hydrogen looks to be a power source of the future. Phil Kreveld looks into all its possibilities, including transport, manufacturing and more.

Hydrogen, the lightest element in the atomic table, earned itself an undeserved, bad rap when world’s largest hydrogen-filled dirigible, the Hindenburg. Having completed the first transatlantic flight from Frankfurt, Germany to the USA in 1937, it burned as it was mooring at Lakehurst naval station, New Jersey on 6 May.

The gas was described as incendiary by the newsman covering the disaster but in fact hydrogen’s lower flammability limit is four-times higher than that of petrol and two-times that of propane and natural gas.

As a source of energy, it outclasses petrol, propane and methane by a factor of two, at 119MJ/kg (1MJ equals 278Wh).

Hydrogen production

Hydrogen is commonly produced by heating natural gas in the presence of steam and a catalyst to speed the ‘steam-forming’ reaction. The reaction produces carbon monoxide and hydrogen.

The carbon monoxide can then be further reacted with water to produce more hydrogen and carbon dioxide. This process is called ‘grey’ hydrogen on account of the carbon dioxide emitted (a ton of hydrogen releases around 10t of carbon dioxide). By using carbon capture ‘blue’ hydrogen can be produced.

Compared to using coal and petroleum products there are more processes which results in additional carbon monoxide or dioxide production.

Hydrogen is also produced by using electricity in the electrolysis of water which represents about 3% of total hydrogen production. Electrolysis requires moderate temperature (50°C typically) as compared to steam reforming processes (800°C).

If renewable electricity sources are used in the electrolysis, so called ‘green’ hydrogen is created. The maximum production efficiency for green hydrogen requires 39KWh for 1kg of hydrogen (a ratio of 84% energy conversion efficiency). However, the energy required to construct the electrolysis cell has not been taken into consideration.

The techniques for electrolysis include:

• Polymer electrolyte membrane (PEM): Hydrogen ions move through the membrane to the cathode where they combine with electrons (flowing through the external circuit) to form hydrogen gas.
• Alkaline: Hydroxyl ions move through the alkaline electrolyte, generating hydrogen at the cathode.
• Ceramic: Water at the cathode combines with external circuit electrons to produce hydrogen and negative oxygen ions. The electrolyser operates at temperatures of around 800°C.

Green hydrogen

Making green hydrogen, given the world’s preoccupation with greenhouse gas emissions, appears to be a no brainer.

There are, however, practical matters. For example, the electrolysis process requires constancy of electricity supply. Hydrogen isn’t produced instantaneously on ‘switch-on’, and depending on the electrolyser used, an hour might pass before full flow of the gas is established. This makes the production by using solar panels less efficient because of their fluctuating power.

Various research papers consulted for this article describe the problem of voltage regulation, varying with maximum power point trackers of solar panels and different voltage requirements for the electrolyser. For commercial purposes, an electrolyser plant could, of course, use grid energy purchased from renewable sources with combined constancy of wind and insolation. Notwithstanding the above, electrolysis is not likely to take over from the steam forming process any time soon.

To make hydrogen an acceptable fuel or energy carrier in the climate of atmospheric carbon dioxide reduction as a priority, carbon dioxide capture must be a commercial reality.

Marubeni and Kawasaki Heavy Industries are working with AGL to produce hydrogen and store carbon dioxide in Bass Strait’s Pelican Field. However, success of commercial carbon capture has so far evaded the world. Australian ingenuity supplied by a company, Calix Ltd in Maddingley, Victoria has produced a pilot carbon capture plant for Belgian cement maker, Lixhe—so a home-grown solution for blue hydrogen remains a possibility.

Green hydrogen projects are mooted for Queensland. The first one is to be developed by Elvin Group Renewables and Denzo Group Australia, producing hydrogen from electricity generated by a solar farm in Bundaberg. There is also a small project, part ARENA-funded which will be part of a renewable microgrid in the Daintree. The hydrogen produced from an electrolyser powered by solar panels will be used ‘electrically’—most likely, filling cylinders for use in power stations as hydrogen is often the coolant of choice for synchronous generators with ratings exceeding 200MW.

Hydrogen for transport

Hydrogen as a fuel can be used in internal combustion engines (ICE). Some car makers argue this produces superior performance compared to fuel cells powering electric motors. As purely hydrogen fuelled, ICE performance is characterised by lower power compared to diesel or petrol, in part because, as a gas, it has a low volumetric energy density at atmospheric pressure and temperature.

However, hydrogen can be a good adjunct to superior engine performance, for example increasing the hydrogen to carbon ratio of the fuel by injecting small amounts of hydrogen into a diesel engine, can improve the consistency of the diesel fuel spray and reduce the combustion duration.

Hydrogen for use in fuel cells to replace the use of batteries in EVs is not a new application for the element but fuel cell technology for vehicular transport is still a nascent one. Even so, there are plenty of hydrogen fuelled commercial and private use vehicles in the market, including those tested by the USA’s National Renewable Energy Laboratory (NREL) and the Department of Energy, including General Motors (GM), Honda, Hyundai, Mercedes-Benz, Nissan and Toyota.

There are also other cars, Hyundai NEXO and Toyota’s Mirai, which, although not tested through above-mentioned regimes, can be considered of good quality.

Hydrogen fuel cells for vehicular use comprise of a polymer electrolyte membrane (hydrogen ion exchange medium), catalyst and anode and cathode. On the anode side, the platinum catalyst enables hydrogen molecules to be split into hydrogen ions and electrons. On the cathode side, the platinum catalyst enables oxygen reduction (adding electrons) by reacting with the hydrogen ions generated by the anode and producing water.

Each individual cell produces less than 1V under typical operating conditions (as opposed to 2.7V for lithium battery cells), therefore requiring them to be stacked on top of each other for a usable output voltage. Each cell in the stack is sandwiched between two bipolar plates to separate it from neighbouring cells. These plates, which may be made of metal, carbon or composites, provide electrical conduction between cells, as well as providing physical strength to the stack.

Fuel cells or fool cells

Elon Musk of Tesla refers to “fool cells”, dismissing the use of hydrogen for cars. Yet, battery-powered vehicles suffer from low energy density (0.567MJ/kg for the Tesla battery) with the Model S having a battery weighing 540kg to provide a large cruising range.

The compression of hydrogen requires pressures of the order of 8,000psi and higher, requiring tanks weighing 150kg storing 5 to 6kg of hydrogen, and providing a driving range of typically 400km (of the same order as a Tesla S).

Currently, the money continues to be on the battery-powered cars with many countries, including Australia, rolling out networks of fast chargers.

One argument against green hydrogen is its overall conversion efficiency (well to wheel). Electrolysis, first place has a maximum efficiency of 80% (discounting sunlight/wind energy in which case it has no marginal cost), 80% in transport, 80% in compression, 80% maximum conversion in the fuel cell and 80% in electrical energy to mechanical energy for a total efficiency of 33%.

This is not necessarily a fair comparison as both means of energy, in order to be ‘green’ have the same sunlight to electricity conversion efficiency. For example, with batteries, electrical losses in transmission and distribution being about 5%, battery charger losses, and battery losses (charge-discharge cycles) as well as battery disposal costs. Fast charging also require, in many cases, changes to networks as power requirements increase (charging 50kW-hr in ten minutes is 300kW in power).

Australia having waved goodbye to its car industry, might restart a smaller form of it with EVs. The Elvin and Denzo alliance, in partnership with H2X, a developer of hydrogen-fuelled vehicles intends to start with the construction of an 80MW hydrogen electrolyser to provide clean energy for H2X vehicles. The use of hydrogen in mining trucks, heavy road transport, replacement of diesel electric trains and public transport is a sensible application as it confines the need for a multiplicity of hydrogen refuelling stations. For a personal transport, refuelling although as fast as for petrol or diesel, requires fleets of tankers suitable for cryogenic transport (at -252°C).

Sunshine for steel and a greener future

A major application of hydrogen is in blast furnaces for steel making, the chemical processes for coking coal and hydrogen are similar, consuming similar weights of coal and hydrogen per ton of steel produced. Furnaces using hydrogen often have an associated plant producing a mixture of hydrogen and carbon monoxide, basically a ‘grey’ process.

Proposals by Dr Ross Garnaut, an Australian leader in green energy, are based on pure hydrogen produced by electrolysis, and for use in blast furnaces as a means of gaining export dollars for our sunshine.

Transport is Australia’s third largest source of greenhouse gas emissions at 96 million tons of carbon dioxide (equivalent) per year and accounts for 17% of total emissions. Electricity accounts for 540 million tons.

These emissions have grown more than any other sector and cars are responsible for roughly half of all transport emissions. It underscores the importance of greener personal and commercial vehicles and provide good reason to focus on hydrogen as well as on battery storage.