Download PDF Winter Bridge on Frontiers of Engineering December 15, 2022 Volume 52 Issue 4 From novel applications of microbes to DEI in engineering to the potential for hydrogen energy, Frontiers of Engineering participants tackle today’s challenging world issues. The winter issue of The Bridge showcases research by early-career engineers as shared at the 2022 US FOE symposium. The Power of Being Negative: Producing H2 and Sequestered Carbon from Biomass and Waste Resources Wednesday, December 14, 2022 Author: Joshua A. Schaidle, R. Gary Grim, Huyen N. Dinh, and Robert M. Baldwin Hydrogen can help decarbonize the economy, especially for the transportation, manufacturing, and chemicals sectors. Low-carbon hydrogen (H2) can be generated through a number of pathways, including steam methane reforming coupled with carbon capture and sequestration (CCS), water electrolysis using renewable electricity, methane pyrolysis, and biomass and waste conversion. However, only the last of these offers a route to carbon-negative H2 when coupled with CCS, thus providing both a service to the environment through carbon dioxide removal from the atmosphere and a valuable downstream product in H2 (figure 1a). Carbon-negative hydrogen is defined as H2 produced with a lifecycle carbon intensity below zero. As one specific example, the carbon intensity of H2 produced from biomass gasification with CCS has been reported as about −13 kg CO2-equivalent/kg of H2 (Al-Qahtani et al. 2021; Susmozas et al. 2016). If it were possible to meet global H2 demand (ca. 76 million metric tons per year) with carbon--negative H2, nearly 0.8 billion tons of CO2 emissions per year could be avoided and another 1 billion tons of CO2 per year removed (figure 1b). For comparison, global CO2 emissions are greater than 35 billion tons per year. Thus, carbon-negative H2 could enable transformation of the worst CO2-emitting processes, such as ammonia synthesis, into carbon sinks—highlighting the power of being negative. Owing to its negative -carbon intensity, this concept falls within a broad array of negative-emissions (or carbon dioxide removal, CDR) technologies, whereby CO2 is removed from the atmosphere and durably stored in geological, terrestrial, or ocean reservoirs, or products (NASEM 2018). Depending on the feedstock, carbon-negative H2 can be included in the class of CDR technologies called biomass carbon removal and -storage, whereby the intrinsic value of biomass is seen as its stored carbon rather than its energy content. This pivot in thinking changes the approach to technology development, with carbon-negative H2 being cited as a key component to achieving carbon neutrality in California by 2045 (LLNL 2020). Biomass Feedstocks and Conversion Technologies Potential biomass and waste feedstocks span terrestrial biomass (i.e., woody and herbaceous biomass, energy crops, agricultural and forest -residues), biogas, algae, food waste, wastewater, waste plastics, and municipal solid waste; and a multitude of technologies, from early-stage to commercial, are available to convert these feedstocks into H2 (figure 1c). These technologies include thermochemical, biochemical, electrochemical, and plasma pathways, and can be divided into two broad categories: direct and indirect. For direct routes, H2 is produced directly in a single conversion step; for indirect routes, an intermediate product (e.g., ethanol or bio-oil) is first formed and then undergoes secondary upgrading to generate H2. The two most common and most mature technologies are direct hydrocarbon reforming and gasification, both of which rely on high temperatures to produce H2 and other intermediates. These technologies are commercially available and represent promising near-term options for deployment of carbon-negative H2 when paired with sustainable feedstocks such as biogas, renewable natural gas, or biomass. But the high-temperature processes also face drawbacks such as high energy demand (e.g., heat) and scalability, especially downscaling to align with local feedstock availability. Early-stage, emerging pathways such as microbial wastewater oxidation, sea-water electrolysis, and plasma activation offer potential solutions, but require research and development to prove out the underlying technology with concurrent derisking of scale-up and integration. Challenges and Benefits of Carbon-Negative Hydrogen While a substantial opportunity exists for both avoiding CO2 emissions and removing CO2 from the atmosphere through carbon-negative H2, important challenges need to be considered: From a logistics perspective, the carbonaceous feedstock, CO2 sequestration site, and H2 off-take need to be colocated or at least reachable through transportation infrastructure (e.g., pipelines). This is termed the “tri-location” challenge. Competition for renewable resources (e.g., biomass) is expected to intensify and will affect supply and demand dynamics, leading to opportunities for technologies that can use low-value, large-scale feedstocks. Biomass and other carbonaceous waste feedstocks are typically heterogeneous and complex (figure 2). This complexity transcends molecular, meso-, and macroscales. Owing to this complexity, converting biomass and other waste feedstocks can be expensive. As an example, for the production of liquid transportation fuels, the refining of petroleum (excluding extraction) can cost about $0.6/gallon, while the conversion of biomass into a biofuel is estimated at $2–$5/gallon (DOE 2020). Looking more specifically at the levelized cost for H2 production, biomass gasification with CCS is estimated at $3.5–$4/kg H2 (nth plant assumption), whereas steam methane reforming of fossil natural gas with CCS is $1.5–$2/kg H2 (IEA 2022; NETL 2022; Shahabuddin et al. 2020). Considering incentives through the US Inflation Reduction Act and assuming a carbon intensity of −13 kg CO2-equivalent/kg of H2, carbon-negative H2 could receive a tax credit of about $1.1/kg H2 under the Carbon Sequestration Tax Credit 45Q or $3.0/kg H2 under the Clean H2 Production Tax Credit 45V (note that these credits are not stackable). As a CDR technology, carbon-negative H2 leveraging of biomass and waste resources can be more complicated in terms of monitoring, reporting, and verification when considering additionality, durability, and leakage (Carbon Direct and Microsoft 2021), as compared to solely technological solutions like direct air capture coupled with geological CO2 storage. Notwithstanding these challenges, carbon-negative H2 can play a key near-term role in the transition to a net-zero emissions economy by (i) enabling decarbonization of industries that use H2 as a chemical feedstock and (ii) removing CO2 from the atmosphere. Carbon-negative H2 may play a key role in the transition to net-zero emissions by removing CO2 from the atmosphere. Importantly, use of carbon-negative H2 can be applied synergistically with other industrial decarbonization strategies (e.g., renewable heat and high-efficiency separations) to achieve even deeper emissions reductions (e.g., through its use to produce sustainable aviation fuel via hydroprocessing of fats, oils, and greases). Realization of this potential will depend on a concerted multifaceted approach to address critical knowledge gaps and expand the technology pipeline. It is also important to consider possible pitfalls of carbon-negative technologies, like creating a “perverse incentive” to use more H2 than needed. Moving Forward To understand technology trade-offs and guide future research and development, comprehensive and rigorous life-cycle environmental, socioeconomic, and energy justice analysis of the carbon-negative H2 pathways (especially beyond reforming and gasification), coupled with evaluation of feedstock supply chains and end-use scenarios for H2 and captured carbon, are needed. To identify integration challenges and derisk commercialization, end-to-end pilot-scale demonstrations, combined with multiscale computational modeling of mature carbon-negative H2 technologies like gasification, must be performed. Finally, there is an expansive opportunity space for early-stage technologies to contribute to carbon--negative H2 production, especially those that offer overall efficiency gains, can more readily use renewable energy inputs, and generate durable carbon products (as opposed to solely CO2 for sequestration). One possible scalable concept for the future that leverages advances in electrochemistry, materials science, and biomass processing is electrochemical reforming of biomass-derived intermediates such as sugars and alcohols (Dolle et al. 2022). This concept has the advantages of modularity, direct use of renewable electricity, liquid feedstocks, and membrane-enabled in situ separations of H2 and CO2 (or other carbon products). Although this technology offers the potential to overcome many of the challenges noted, it is still in its infancy. Thus, the community needs to pull together and map out “the adjacent possible” (Johnson 2010) in the field of carbon-negative H2. Considering the opportunity space for carbon--negative H2 and its projected benefits, shouldn’t we harness the power of being negative? Acknowledgments This work was authored by the National Renewable Energy Laboratory, operated by Alliance for Sustainable Energy, LLC, for the US Department of Energy (DOE) under Contract No. DE-AC36-08GO28308. The views expressed in the article do not necessarily represent the views of the DOE or the US government. References Al-Qahtani A, Parkinson B, Hellgardt K, Shah N, Guillen-Gosalbez G. 2021. Uncovering the true cost of hydrogen production routes using life cycle monetization. Applied Energy 281:115958. Carbon Direct and Microsoft. 2021. Criteria for High-Quality Carbon Dioxide Removal. New York. Ciesielski P, Pecha M, Lattanzi A, Bharadwaj V, Crowley M, Bu L, Vermaas J, Steirer K, Crowley M. 2020. Advances in multiscale modeling of lignocellulosic biomass. ACS Sustainable Chemistry and Engineering 8(9):3512–31. DOE [US Department of Energy]. 2020. R&D 2020 State of Technology (DOE/EE-2531). Washington: Office of Energy Efficiency and Renewable Energy, Bioenergy Technologies Office. DOE. 2022. Carbon Dioxide Removal Fact Sheet. Washington: Office of Fossil Energy and Carbon Management. Dolle C, Neha N, Coutanceau C. 2022. Electrochemical hydrogen production from biomass. Current Opinion in Electrochemistry 31:100841. Johnson S. 2010. Where Good Ideas Come From: The Natural History of Innovation. New York: Penguin Group. IEA [International Energy Agency]. 2022. Global average levelised cost of hydrogen production by energy source and technology, 2019 and 2050. Paris. LLNL [Lawrence Livermore National Laboratory]. 2020. Getting to Neutral: Options for Negative Carbon Emissions in California (LLNL-TR-796100). Livermore CA. NASEM [National Academies of Sciences, Engineering, and Medicine]. 2018. Negative Emissions Technologies and Reliable Sequestration: A Research Agenda. Washington: National Academies Press. NETL [National Energy Technology Laboratory]. 2022. Comparison of Commercial, State of the Art, Fossil Based Hydrogen Production Technologies (DOE/NETL 2022/3241). Albany OR. Shahabuddin M, Krishna B, Bhaskar T, Perkins G. 2020. Advances in the thermo-chemical production of hydrogen from biomass and residual wastes: Summary of recent techno-economic analyses. Bioresource Technology 299:122557. Susmozas AI, Iribarren D, Zapp P, Linssen J, Dufour J. 2016. Life-cycle performance of hydrogen production via indirect biomass gasification with CO2 capture. International Journal of Hydrogen Energy 41(42):19484–91.  US Energy Information Administration, Gasoline and Diesel Fuel Update, Aug 2022 (https://www.eia.gov/petroleum/-gasdiesel/). About the Author:Josh Schaidle is lab program manager for carbon management, Gary Grim is a researcher, Huyen Dinh is Distinguished Member of the Research Staff, and Robert Baldwin is principal scientist, all at the National Renewable Energy Laboratory.