June 15, 2023
The webinar featured discussions on the potential of hydrogen as a clean energy carrier and its various applications. Nebojsa Nakicenovic highlighted the evolution of energy systems towards higher hydrogen to carbon ratio and universal electrification. He emphasized the promise of electricity and hydrogen as complementary energy sources in a decarbonized world energy system, in the future hydricity age. However, several challenges need to be addressed for their widespread adoption. Marcel Van de Voorde discussed different methods of hydrogen production, storage, and usage, focusing on zero-carbon (green) hydrogen production through electrochemical reactors. The importance of developing suitable materials for hydrogen storage was highlighted. The diverse applications of hydrogen were also explored. Education and research are identified as critical factors for the advancement of the hydrogen economy. Richard B. Hoover presented the discovery of a non-pathogenic bacterium, Spirochaeta americana, capable of producing hydrogen through fermentation. Elena V. Pikuta explained the potential of bacterial hydrogen production in transitioning to non-polluting energy sources, particularly in the transportation sector. The remarkable hydrogen production levels exhibited by S. Americana were discussed, along with the prospects of industrial-scale bio-hydrogen production. Overall, the webinar shed light on the challenges and opportunities associated with hydrogen as a clean energy solution.
Vice President, World Academy of Art and Science
Honorary Emeritus Scholar, International Institute for Applied Systems Analysis; Former Tenured Professor of Energy Economics, Vienna University of Technology, Austria; Vice Chair, Group of Chief Scientific Advisors, European Commission
Future energy (sources) transformation
Hydrogen is increasingly being viewed as an important energy carrier of the future due to its unique properties. It produces only water vapor when combusted with oxygen and some NOx with air. It can be stored in gaseous or liquid form, and it is relatively easy to transport in either form. If produced from carbon-free energy sources, its use does not result in greenhouse gas emissions. Thus, it should not be surprising that it is now over half a century that hydrogen has been seen as the clean and convenient energy carrier of the future, especially when generated from renewables or nuclear energy sources. In fact, both of those sources of energy require storable energy carriers, renewables because they are intermittent and nuclear for peak demand above the baseload.
Interestingly, the historical evolution of the energy systems is in the direction of ever higher hydrogen to carbon ratio as fuelwood was substituted by coal and later coal by crude oil and natural gas, a trend from solids to liquids and gases. The other pervasive evolutionary change is toward universal electrification. Thus, electricity and hydrogen, “electron and proton”, hold the promise of being clean and convenient complementary energy carriers of the decarbonized world energy system, in the future hydricity age. Furthermore, they could be easily converted one into another providing flexibility for an ever-more digitalized future. However, there are several challenges to overcome in order to fully realize potentials of hydrogen as complementary energy carrier to electricity. The main one is the need to invest into new infrastructures to produce, transport, store, and use hydrogen. These are similar challenges as for electrification.
Today, only about one percent of global energy reaches the end use in the form of hydrogen and most of it is produced through steam-reforming natural gas. Other source is electrolysis increasingly from renewables, especially to store the excess electricity generated on a windy or sunny day, when demand is low. In terms of opportunities, there is potential for hydrogen to be used in a variety of applications, for example, to reduce iron or as a feedstock without carbon dioxide emissions, with fuel cells in zero-emissions aircrafts, ships, and long-haul road transport.
Hydrogen is the most abundant element in the Universe, and on the Earth all large molecules contain hydrogen. It is the lightest gas, has the lowest viscosity among fluids and a very high heat conductivity and specific heat capacity, and is the most energy-dense fuel by mass, even though has the lowest energy density per unit volume. The combustion of an equivalent weight of hydrogen releases three-times and seven-times more energy than gasoline and coal, respectively. As a fuel, it produces only water, and is thus perfect to help combat climate change. The current unprecedented political and business interests for hydrogen worldwide is related to the fundamental role assigned to reach a climate-neutral and zero-pollution economy by 2050. This contribution will mainly deal with the following three aspects.
Hydrogen gas is rare on the Earth, and therefore, it must be produced. Today, more than 95% of H2 (gray hydrogen) is produced from fossil fuels (natural gas, oil, and coal), and in Europe mostly by methane steam reforming:
CH4 + 2H2O → 4H2 + CO2.
Zero-carbon green hydrogen is produced by energy intensive water conversion to hydrogen and oxygen, performed inside electrochemical reactors (electrolysers). Hydrogen today accounts for less than 2% of the generated world energy. Moreover, the gray hydrogen cost is today only 1–1.5 euro/kg, and the green hydrogen cost is quite fastly decreasing from 4–5 to around 2.5 euro/kg. However, gray hydrogen gives roughly 10 kg of CO2 per kg of H2 from methane and 3 times more from coal. The necessity of a storage system for hydrogen is an essential issue. A great variety of solutions were suggested, from underground/undersea systems, via salt caverns, to chemicals such as ammonia and various materials. Storing hydrogen in large quantities will be one of the most significant challenges for a future hydrogen economy.
The most popular green hydrogen would be used to enable mobility, supply electricity and heat, and decarbonize chemicals, cement, and steel, as well as in vehicles as a fuel for internal combustion engines or as a feed for fuel cells, which produce electricity to power electric vehicle motors. Not less important critical issues for the development of the hydrogen economy are international cooperation, education, and research, standardization of infrastructures and safety regulations, and financial instruments as well as decarbonization of political decisions.
Elena V. Pikuta
Astrobiology Laboratory, National Space Science and Technology Center, National Aeronautics and Space Administration, Huntsville, AL, USA
Bacterial hydrogen production
Bacterial production of hydrogen may play an important role in the future transition from reliance on fossil fuels to renewable, non-polluting clean source of energy. Hydrogen gas could be used as a clean energy source for many economic sectors, including transportation. Greenhouse gases trap heat and contribute to climate change, and the transportation sector is responsible for 29% of this emission. Bacterial hydrogen has the potential to significantly reduce air pollution from trucks, buses, planes, and ships. In natural ecosystems, hydrogen-producing bacteria occur in close association with hydrogen-consuming microorganisms. Both, the producers and consumers of the hydrogen gas are equipped with specific enzymes – hydrogenases, which have a very high affinity for hydrogen molecules, located in periplasmic space of cell wall. Hydrogenase is the key enzyme of the energetic metabolism in cells, it catalyzes converse reaction of hydrogen oxidation: H2 = 2H+ + 2e–, and is responsible for the consumption and excretion of hydrogen.
Alkalispirochaeta americana ASpG1T was isolated from alkaline Mono Lake at Mojave Desert, in California. This Gram-negative, free-living, non-pathogenic spirochete requires anaerobic buffer system with pH 9.0–10.0 and 3% NaCl (marine salinity) for growth. It was isolated as a satellite of the hydrogen consuming sulfate-reducing bacterium (SRB) Desulfonatronum thioreducens MLF1T. In vitro these bacteria grow better in binary culture since SRB removes inhibiting concentrations of hydrogen for sugar-lytic spirochete. For industrial applications, Gram-negative bacteria are preferable since no spore-formation occurs during continuing batch cultivation. Also, the yield of H2 from A. americana ASpG1T may achieve 80% compared to ~30% of those by Clostridium butyricum and other pathogenic anaerobes. At application of A. americana ASpG1T, the anaerobic mixture of exit gases (H2:CO2) appears in safe, not explosive proportion, while commercial cultivation of hydrogen-producing photosynthetic algae yields explosive gas mixture of hydrogen and oxygen.
Richard B. Hoover
US Space & Rocket Center, Huntsville, AL, USA
Potential applications of Spirochaeta americana for hydrogen production
The global climate and energy crisis has highlighted the urgent need for clean, decarbonized energy production and stimulated interest in renewable, sustainable sources. The International Energy Agency sees hydrogen as a key part of the energy transition and green biohydrogen may play an important role. Hydrogen stores the highest chemical energy per unit mass (higher heating value – 142 MJ/kg) and yields pure water upon reaction with oxygen. In 2000, a National Space Science Technology Center (NSSTC) astrobiology expedition searched for microbial extremophiles in sulfurous, alkaline, hypersaline, endorheic soda Mono Lake in California – as analog for impact/volcanic crater lakes on Mars. Paoha, a volcanic island with hot (~90 oC) alkaline springs emerged 350 years ago in Mono Lake. Hoover anaerobically collected black mud samples with strong hydrogen sulfide odor from under shallow water (T – 21.6 oC; salinity – 7%; pH – 9.9) at the southshore. Pikuta obtained enrichment cultures and isolated the novel strain ASpG1T – an obligately anaerobic, mesophilic, haloalkaliphilic, non-pathogenic, sugar-lytic spirochaete. The new species Spirochaeta americana ASpG1T was validly published in 2003 and transferred in 2017 to new genus as Alkalispirochaeta americana ASpG1T.
Characterization studies showed that S. americana is a strictly anaerobic chemoheterotrophic, obligate haloalkaliphile (no growth at pH 7) requiring carbonate and sodium ions. It exhibited fermentative type metabolism with hydrogen as the primary end product of D–glucose fermentation. Subsequent NSSTC batch cultivation experiments (T – 37 oC; pH – 9.7; NaCl – 3% w/v) revealed an astonishing level (~80–90%) of hydrogen production during the first 29 hours of growth with minor (~1%) CO2 levels produced. Growth at high pH prevents contamination by methanogens. Spirochaeta americana is non-pathogenic unlike Klebsiella, Enterobacter, Clostridium species. Batch culture experiments showed best hydrogen production with addition of 0.5–1.0 g/lyeast extract. Removing inhibiting concentration of hydrogen from the system maintains culture in good physiological state.