Green Hydrogen Generation Technologies- A Ring Side View

The Hydrogen Economy hinges on technology advancement to reduce costs of manufacturing, transportation, safety and infrastructure development.

June 04, 2024. By News Bureau

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Hydrogen economy

Nauvata Energy Transition

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In 1875, Julies Verne, in his book, The Mysterious Island, wrote “water will one day be employed as fuel, that hydrogen and oxygen which constitute it, used singly or together, will furnish an inexhaustible source of heat and light, of an intensity of which coal is not capable.” Little did he know that his prophecy would be delayed by one and a half century by Edwin Drake who had spudded his first oil well in 1859 in Pennsylvania!

That hydrogen future seems to be arriving only now – out of necessity perhaps, to achieve Net Zero by 2050. Green hydrogen would constitute 7-12% of the energy mix by 2050. The “medium” to “high” confidence use-cases for hydrogen are in:

Green Steel Manufacturing through the H2-DRI-EAF route: The DRI process produces 0.08t CO2/t of steel compared to 0.77t CO2/t of steel using Natural Gas or 1.87t CO2/t of steel using coal.

Decarbonizing heavy-duty long distance transport using H2 fuel-cells: Grids’ limitation to fast-charge thousands of EV trucks at the same time plus 8-10 times more charge points, and the impact of the weight of heavy batteries, make H2 fuel-cells a preferred option for this sector.

LNG remains the transition fuel for both the above cases.

Where possible, green hydrogen can replace ~100 mtpa of dirty hydrogen that is being used now for making ammonia for fertiliser, methanol and oil refining.

The Hydrogen Economy hinges on technology advancement to reduce costs of manufacturing, transportation, safety and infrastructure development. At present India cannot afford the Hydrogen Economy due to the costs: Green H2 production costs are in the range of $4-7/kg globally, except China. Hydrogen at $2/kg is equivalent to $15/MMBtu of LNG. $4-7/kg H2 translates to an LNG equivalent of $30-50/MMbtu! Compare this with our existing LNG import contracts that are in the range of $7-11/MMBtu.

Technology, economies of scale, commoditization and digitalization will reduce cost. From FOAK (first of a kind) to NOAK (n^th of a kind) there is always a cost reduction. For electrolysers, the learning rate (rate of cost reduction for each doubling in cumulative installed capacity) is ~11-13%. Given that Solar PV saw a learning rate of 23-25%, Lithium Ion batteries 20% and wind turbines 15 %, the learning rate for electrolysers can only improve.

Cost of hydrogen/kg consists of 50-60% electricity, 25-30% Capex and the balance as Opex and Abex. By 2030-35, if the Capex for electrolysers stack and BOP (Balance of Plant) comes down to $150/Kw-$250/Kw, RE is @ $20/Mwh, efficiency is consistently >80%, Opex at 1-2 % of the Capex, then Green Hydrogen can be produced at $1 to $1.5 /kg. This is competitive with grey hydrogen.

Technologies for production of Green Hydrogen are broadly classified in the following categories:

Water-splitting processes (through Electrolysis, Thermolysis and Photolysis)
Biogenic hydrogen using biological and thermochemical processes.
Extraction of naturally occurring hydrogen from the earth’s crust (White Hydrogen).

Electrolysis - The most prominent technologies are Alkaline-Electrolysers, PEM, SOEC, and AEM. Electricity from Solar, Wind or Hydropower make the hydrogen produced from these technologies green.

Alkaline Water Electrolyser (AWE) has been around for over 100 years – it operates at low temperature 30-80 deg C. It uses concentrated alkaline solutions (5M KOH/NaOH). The electrodes are nickel coated and asbestos/ZrO₂-based diaphragm is used as a separator.

Technological improvements are focussed on reducing costs (from the current system cost of 500-900$/Kw to ~150$/Kw), improving purity of hydrogen and durability. Focus areas for improvement are the following:

current density (from the current 0.8A/cm2 to 2-3A/cm2),
poor part-load performance with fluctuating RESs; they operate best when at or near their rated capacity.
- risk of gas-crossover (hydrogen and oxygen mixing) increases when operating at low power, especially if impurities are present. As a safety measure, the electrolyser is shutdown in the low power range. It takes almost an hour to get the electrolyser from cold start to full operating speed (compared to five mins for PEM electrolyser).
- high ohmic resistance due to use of thick diaphragms impacts performance at low currents. Highly porous diaphragms can lead to gas crossover.
cell efficiency - ranges from 55-75%; keeping it consistently above 75% is key. Cell voltage optimization has a direct impact on cell efficiency.
concentrated KOH is toxic; needs replacement every 2-4 years. Handling large amounts of KOH has safety risks. Better filtration systems to reduce the frequency of change out will be key. High water consumption also needs to be dealt with.

Alkaline electrolysers are commonly used due their low cost but with the right performance and safety trade-offs. Shell’s 200 MW HH1 project (one of the largest so far) under construction in Rotterdam, uses AWE.

Anion Exchange Membrane (AEM) Electrolyser: This technology is at a pilot level. The main difference with Alkaline Electrolysers is the use of Anion Exchange Membrane instead of conventional asbestos diaphragms. Unlike the high concentration KOH electrolyte in Alkaline Electrolyser, AEM uses distilled water or low concentration alkaline solution (1M KOH). Commercial application is challenged due lower duration of stable operation and less than 60% cell efficiency.

Proton Exchange Membrane (PEM) electrolysers: PEM offers several advantages over alkaline water electrolysis such as high operating current density(1-2A/cm2) , high purity of gases(99.999%), higher outlet pressure (30-35 bars),60-85% efficiency and smaller footprint ( containerized electrolyser stack and 60-80% of BOP; typically 400Kw to 1Mwh modules) – These containers are stacked up for larger capacity. This simplifies constructability. Use of highly active Platinum electrodes and lower pH of the electrolyte improves kinematics helps to speed up reaction. Lower operating temperatures (30-80 deg C) and the absence of caustic electrolytes make operations safer for PEM electrolysers.

To reduce cost and improve performance, following are the technology focus areas:

Membranes- membranes with stronger mechanical resistance and reduced thickness will improve longevity and increase efficiency leading to lower electricity consumption.
Electro-catalyst Materials —Use of precious materials (Platinum/Iridium Oxide) makes PEM costlier than others. Reduced iridium-loading using nanoparticulate catalysts /appropriate catalyst support, while enhancing conductivity would reduce costs from the current USD 1000-1600/Kw to ~USD 200/Kw by 2030-35.

Solid Oxide Water Electrolyser: This technology is at TRL6 (waiting to be commercialized) but holds significant promise as a high efficiency electrolyser. It operates with water as steam at elevated temperatures of 500 – 850 deg C; this aids the splitting of water with a lower power consumption. Further, there is no exotic metallurgy involved. It has essentially three components – a dense ceramic electrolyte (YSZ: yttria established zirconia is commonly used) which conducts oxide ion (O2-) and anode (typically perovskite materials) and cathode (typically porous ceramic materials YSZ or Ni-YSZ).High operating temperatures lead to improved thermodynamics and reaction kinematics, which boosts up the overall efficiency of the system up to 90%.

Current limitations on its long-term stability (stable operation only for 20,000h) and high cost electrolyser ($2000+/Kw) despite the use of non-noble metal catalysts.

Photo-electrolysis/photolysis: Photochemical splitting of water has been tested at pilot scale (EPFL Campus Switzerland has the largest constructed to date: ½ kg hydrogen in eight hrs; ~2Kw of equivalent output power). Sunrays are concentrated and used as the energy source to produce oxygen and hydrogen. Photoelectrode is made of semi-conducting material that absorbs solar energy and generates voltage that causes a current flow that performs water electrolysis. Current density: 10-30mA/cm2.

Photoelectrode with precise nanostructures makes the technology very complex and costly to scale up. Efficiency of light absorption is also an issue that needs further research.

Thermolysis/Thermochemical splitting (TCWS): At high temperatures of ~2200 deg C, roughly 3% of the water splits into O2 and H2; 50% at 3000 deg C. Concentrated Solar Energy and waste heat from Nuclear Reactor could be the energy source. However, TCWS is carried out at lower temperatures: 500-2000C, in a series of chemical reactions using appropriate chemicals. It works in a closed loop cycle in which only water is consumed. Commercialization is inhibited by prohibitive costs, system design and economic yield limitations.

White Hydrogen: Naturally occurring Hydrogen. In Bourakebougou, a small village in Mali, hydrogen from a well powers shops and homes. In Lorraine, France, 46 – 260 mmt reserves of Hydrogen have been established beneath the abandoned coal mines. US, Australia, Africa and Russia have all reported hydrogen reserves.

Multiple hypothesis have been put forth:

Radiolysis: Water is split into hydrogen and oxygen by the energy from the radioactive rocks. Hydrogen trapped in the pore spaces of these rocks can be produced by drilling into them.
Serpentinisation: Iron-rich rocks (ferromagnesian rocks – olivines and pyroxenes) buried in mid ocean ridges and in the continental shelfs, react with very hot water to produce iron oxide and hydrogen. Understanding the efficacy of H2 production by fracturing these rocks with water is an area of research.
Deep-seated formation: Earth’s core has hydrogen. Technological breakthroughs would be needed to win it.

Biogenic Hydrogen (Bio-H2) from organic wastes using various cultures of microbes is largely through two microbial pathways: Photo-fermentation (in the presence of light) and Dark-Fermentation (in the absence of light). Anaerobic phototropic and chemotropic microbes metabolize the carbon in the organic wastes and break the long chains into CO2 and Hydrogen. Dark fermentation, photo-fermentation and bio- photolysis have been proven at lab scales.

Dark Fermentation holds promise because of its light autonomous character (can produce hydrogen 24x7) with high-energy efficiency. However, it is limited by economic yield. Fatty acids is a by-product that can undergo bio-methanation to produce biogas. Improvement in microbial strain for scaled up operations, bioreactor design and high yield feedstock are key to supporting commercialization.

Besides the above, there are multiple other indirect pathways to convert waste to hydrogen through synthesis gas routes.

In conclusion, it can be said that with planned capex of UD 350b in hydrogen manufacturing so far, 60-80 GW of electrolyser capacity in the works, folks are no more selling ‘hopium’; Julies Verne’s prophecy may yet come true – not wholly or in full measures but very substantially!

- Baroruchi Mishra, Group CEO, Nauvata Energy Transition (NET) Enterprise Pvt. Ltd.