Green, yellow, blue, gray and now even gold: for a colorless gas, hydrogen is given the whole rainbow of colors. What is green hydrogen and what is an electrolyzer?
Green Hydrogen is a type of hydrogen produced using renewable energy sources, such as wind or solar power. This renewable energy is used to power an electrolyzer that separates water into its component elements, hydrogen and oxygen. The process of producing green hydrogen is referred to as "water electrolysis," and it is considered by many as a key technology to reduce carbon emissions and combat climate change. A lot of people incorrectly equate hydrogen produced with electrolyzers as green hydrogen, but the key definition is that the electrolyzer needs to consume only (well, the vast majority of) renewable energy resources to be called green.
So what’s the buzz around Green Hydrogen?
Green hydrogen is a versatile green molecule that has the potential to decarbonize several industries:
Hydrogen from electrolysis (remember, that doesn’t necessarily mean green!) has been a relatively niche market, representing only around 4% of worldwide hydrogen production (Source: Irena), but ask anyone that knows anything (or nothing) about hydrogen and you’ll hear that most of the “new” hydrogen production will be of the green kind.
This is because of the combination of two things:
Below are the leading electrolyzer technologies and their advantages and disadvantages.
Alkaline electrolyzers are commercially available today even in large capacity installations (>100MW) and operate via transport of hydroxide ions (OH-) through an aqueous electrolyte (typically a solution of sodium or potassium hydroxide) from the cathode to the anode.
NEL Hydrogen, a Norwegian company established in 1927, is a well known electrolyzer manufacturer that commissioned the largest water electrolysis plant in the world using hydropower in 1940 - therefore making Green Hydrogen as early as the 20th century! Decarbonization pressures are making the deployment of Green Hydrogen more urgent and timely than ever, but producing hydrogen from renewable sources is not a novel concept.
Proton Exchange Membrane (PEM) Electrolyzers
A Proton Exchange Membrane (PEM) electrolyzer uses a solid polymer electrolyte (essentially a plastic material) to conduct hydrogen ions (protons) separated at the anode from water. The hydrogen reacts at the cathode with the free electrons (passed from anode to cathode through an external circuit) to form hydrogen gas. Today, PEM is half the installed capacity of Alkaline.
Several startups are focused on developing PEM electrolyzer components, such as membranes, synthetic catalysts, or on developing entirely new electrolyzer stacks altogether. The main objectives are to achieve a CapEX reduction or, most importantly, better efficiencies and better operating parameters (such as the ability to operate the system both in a very low electricity input mode or very high electricity input mode). Companies in the PEM space are Ionomr Innovations and H2U Technologies, which are both developing membranes that do not require expensive Platinum Group Metals (PGM) catalysts to operate. H2U Technologies is also designing a new electrolyzer stack - not just the materials - and is beginning field testing. Companies like Celadyne Technologies are developing innovative membrane materials that increase durability and expand operating conditions of PEM systems. 1s1 Energy is developing a new PEM electrolyzer with the goal of dramatically improving operating parameters, particularly efficiency and current density (therefore enabling a broader set of operating conditions).
Anion Exchange Membrane (AEM) Electrolyzers
Anion Exchange Membranes transport anions (OH-) instead of protons and aim to combine the benefits of alkaline electrolysis (namely a stable, cheap catalyst) with the advantages of PEM electrolysis (particularly the fast dynamic response and higher efficiency and current density). This is a newer technology with promising potential, as it has CAPEX advantages against PEM and better operating parameters than AEM.
Several startups are innovating in the AEM space. Power 2 Hydrogen, Enapter, Arco Technologies and Versogen are all working on and testing AEM designs that can effectively utilize renewable energy with a lower capital cost than PEM. Ionomr, together with their PEM product, is also developing an AEM version of their membrane.
Solid Oxide Electrolyzer Cell (SOEC) Electrolyzers
Solid oxide electrolyzers are a different technology type that uses a solid ceramic material heated at high temperature (~500-800°C) to conduct negatively charged oxygen ions (O2-). Steam introduced with free electrons at the cathode generate the hydrogen gas and negatively charged ions. The oxygen ions pass through the solid ceramic membrane and react at the anode to form oxygen gas and generate electrons for the external circuit. The main advantage of SOECs is their electric efficiency,
Bloom Energy, an established manufacturer of Fuel Cells, is one of the leaders in the development of SOEC designs. Pilot results from Bloom show production rates of 37.7 kWh /kg of Hydrogen produced, compared to 52-54 kWh/kg of typical PEM or Alkaline electrolyzers.
Hydrogen is the glue that holds all of renewable energy together, and Green Hydrogen in particular has the ability to link green electrons with green molecules, building an integrated energy system that is more efficient and more resilient than the sum of its parts.
Questions on the article? Contact us here.