Hydrogen is a chemical element with symbol H and atomic number 1. It is the simplest, most abundant and lightest element in the universe, constitutes about 75% of the universe mass. It was discovered and first documented in 1671 by Robert Boyle and was recognised as an element by Henry Cavendish in 1766. Hydrogen readily combines with other elements to form molecules such as water (H2O), methane (CH4) , ammonia (NH3), methanol (CH3OH), hydrogen peroxide (H2O2) and sugar (C12H22O11). Hydrogen is produced by breaking the chemical bonds in the molecules that form these substances. There are a number of technologies to produce hydrogen from different primary energy feedstock, including fossil fuel, coal, biomass, electricity and the renewables such as sun and wind. At present, most hydrogen is produced from fossil fuels through a process called steam reforming of methane which involves reaction between natural gass with steam to produce hydrogen, carbon dioxide and carbon monoxide. This process generates greenhouse gases and there is a push from all around the world to produce clean hydrogen and has net-zero carbon.

Clean hydrogen can be produced by passing electricity thrugh water to drive a chemical reaction to split water into its components (hydrogen and oxygen) in a process known as 'electrolysis'. The hydrogen is collected and the oxygen is released. If the electricity used for the electrolysis is from renewable sources such as solar and winds, the hydrogen produced is clean and has zero carbon. If fossil fuels with carbon capture and storage is used to produce hydrogen, the hydrogen is said to be produced with low to zero carbon emissions. Electrolysis is a mature technology that can be easily implemented for small or large scale applications. There are different types of electrolysers, with different costs and efficiencies which rapidly developed to improve over time.

Like electricity, Hydrogen is not an energy resource, but is an energy carrier. Energy carriers allow the transport of energy in a usable form from one place to another. Both electricity and hydrogen can be produced from all energy resources available including natural gas, fossil fuels, biomass and renewables. Hydrogen has the highest energy content of any common fuel by weight (about 3x more than gasoline), but it has the lowest energy content by volume (about 4x less than gasoline). Tradtionally hydrogen has been more expensive than conventional fuel to produce, store and transport. However due to high energy content per unit weight, it has been used as rocket fuel and in fuel cells to produced electricity on some spacecraft. The difference is that electricity is made up of electrons only, but hydrogen is composed of molecules and electrons. Due to its molecular structure, hydrogen can be stored for a long period and has potential to replace the current use of fossil fuels. On the other hand, electricity is limited in its uses and has limited storage capabilities. Electricity and hydrogen are not competing, but rather complementary as energy carriers.

The different colour of hydrogen's refer to the various sources and production processes it came from, and offe a type of certification, however, unregulated. Clean hydrogen refer to hydrogen that is produced with very low to zero carbon emissions. The term covers hydrogen produced with and without CCS. The colour terms refer to the 'degree of cleannes' of hydrogen. In Australia, * Brown hydrogen: when it is produced from brown coal and the carbon is released to the atmosphere; * Grey hydrogen: when hydrogen is produced from natural gas and the carbon is released to the atmosphere; * Blue hydrogen: the hydrogen is produced from renewable energy and natural gas but the carbon is not released into atmosphere, but captured and stored; * Green hydrogen: when it is carbon free and hydrogen is produced from renewable energy and non-fossil fuel sources.

Yes. Hydrogen is just as safe as any other transportation fuel (i.e. gasoline, diesel and natural gas). Any volatile substances when combined with an oxidizer (most commonly in air), in the right proportion will ignite to release energy in the form of heat. This is the principles of the conventional internal combustion engines that power our vehicles, heats our homes, cooks our food and uses for steel manufacturing. With the right system design, hydrogen systems can be designed to be no riskier than their conventional fuel counterpart. Hydrogen has been safely produced and used in industry sector for over half century. As with every fuel, safe handling practices are required. Hydrogen is non-toxic and is not harmful to human health or environment when released. Hydrogen codes and standards are in place at national and international level to ensure that hydrogen fuelling stations are as safe as their gasoline counterparts. The Australian Hydrogen Council and Standards Australia are working with other bodies to mirror international standards in Australia and establish the righ regulatory framework.

A fuel cell is an electrochemical device that converts hydrogen and oxygen into electricity. Basically fuel cell works like an electrolyser in reverse. Fuel cell electric vehicle use PEM fuel cell - proton exchange membrane. In its simplest form, a PEM fuel cell consists of two electrodes: the anode and the cathode, separated by a catalyt coated membrane. The catalyst separates hydrogen into its components - a proton and an electron. The proton moves through the membrane to reach the anode, whereas the electron is forces to follow an alternate path which creates usable electricity for the vehicle's motor and other applications. Once the proton and electron reach the anode, they combine with oxygen and eventually create water - and is emitted from the vehicle. To power a car, more than one fuel cell is required to provide enough electricity, hence a fuel cell stack is used. The stack generates electricity that powers the vehicle as long as fuel is supplied.

Hydrogen can be burnt in a fuel cell to generate electricity, and in combustion engine, just like petrol, can be transformed into energy to move a car or produce electricity and/or heat. Some of the key benefits of hydrogen fuel cells are: - More efficient than traditional combustion engine - Lower green house gas emissions during vehicle operation - Quiet operation - Lower chance of breakdown due to fewer moving parts involved - Many different type of applications such as building power, vehicle power - Can be used in conjuction with solar and wind energy technologies for energy storage - Lower emissions of particulate pollutants from car exhaust - No NOx emissions

Power-to-X (P2X) refers to where electricity produced from renewable energy is used to produce clean fuels and chemicals. P2X products cover hydrogen, ammonia, methane, oxyhydrocarbons, hydrogen peroxide and many other derivatives. Read more about 'Opportunities and Challenges for Renewable Power-to-X in ACS Energy Letters (2020), 5(12), 3843-3847: https://pubs.acs.org/doi/10.1021/acsenergylett.0c02249