Sustainable energy: Clean hydrogen for industrial decarbonization

The pursuit of sustainable energy has become an imperative to address the challenges of industrial decarbonization, with clean hydrogen emerging as a strategic solution. This sustainable energy carrier, generated from renewable sources, enables a significant reduction in carbon emissions across energy-intensive industrial processes while offering versatility for storage and transport. Adopting green hydrogen not only drives technological innovation in sectors such as steelmaking, chemicals, and heavy transport but also paves the way toward an industrial model that is more efficient, resilient, and committed to sustainability.

This article unravels the technological pathways of clean hydrogen, the emission intensity thresholds that define its viability, the industries leading its adoption, and strategies to reduce the LCOH (Levelized Cost of Hydrogen) until it achieves competitiveness against gray hydrogen at $1.50–$2.50/kg.

What does energy sustainability really mean in clean hydrogen?

Industrial decarbonization faces a monumental challenge: sectors such as steel, cement, chemicals, and refining account for approximately 25% of global CO₂ emissions but are extremely difficult to electrify. While the world produces 95 million tonnes of hydrogen annually, 97.8% comes from fossil fuels without carbon capture, emitting 920 million tonnes of CO₂ equivalent.

The critical question is no longer whether clean hydrogen is viable, but which technological pathway will reach cost parity first. In 2025, we witnessed an unexpected shift: while green hydrogen remains the media darling and blue hydrogen the established transition option, a third way is emerging with disruptive force. Turquoise hydrogen, produced via methane pyrolysis, has just demonstrated production costs of $0.73/kg in South Korea, challenging the $2.0–$2.5/kg projected for green hydrogen by 2035.

Clean hydrogen in industry: Technological pathways

The concept of “clean hydrogen” has evolved from an ambiguous color-based definition toward precise metrics of emission intensity. U.S. legislation (IRA §45V) stipulates that qualified hydrogen must have life-cycle emissions of ≤4 kg CO₂e/kg H₂, measured from resource extraction to the point of production (well-to-gate) using Argonne National Laboratory’s 45VH2-GREET model.

The European Union is even stricter: its Hydrogen and Gas Market Directive (2024) defines low-carbon hydrogen as ≤3.38 kg CO₂e/kg H₂, equivalent to a 70% reduction versus the fossil comparator of 94g CO₂e/MJ.

To provide context, current gray hydrogen (methane reforming without capture) emits 10–14 kg CO₂e/kg H₂, where upstream methane leaks represent an additional 1–5 kg CO₂e. Blue hydrogen with 60% capture reduces this to 5–8 kg CO₂e/kg H₂, while capture rates $>90\%$ achieve 0.8–6 kg CO₂e/kg H₂.

Green hydrogen from electrolysis using pure renewables theoretically reaches 0 kg CO₂e, although the embodied emissions in the manufacturing of renewable assets can add 0.4–2.7 kg CO₂e/kg H₂, a factor rarely included in current certifications.

Turquoise hydrogen: Superior energy efficiency

Methane pyrolysis (CH₄ → C + 2H₂) represents an energy paradigm shift that the industry is only beginning to grasp. Unlike electrolysis, which requires 60 kWh/kg H₂ (a theoretical 39.4 kWh plus conversion losses), thermal pyrolysis initially consumed 25 kWh/kg H₂ and has now reached 18–20 kWh/kg with optimized heat recovery, according to 2024–2025 commercial plant data. This difference is not trivial: it represents 70% less energy than electrolysis, translating directly into lower operating costs and reduced pressure on the electrical grid.

The 2025 South Korean breakthrough brought the turquoise LCOH down to $0.73/kg through an integrated system combining pyrolysis, CO₂ reforming, and oxygen combustion. In comparison, gray hydrogen costs $1.50–$2.50/kg, blue hydrogen $2.00–$3.50/kg (depending on CCS costs and natural gas volatility), and green hydrogen currently sits at $3.40–$7.50/kg, with projections of $2.0–$2.5/kg by 2035 in favorable markets.

The emission intensity of turquoise hydrogen reaches 0.45–0.91 kg CO₂e/kg H₂ when using Grade A natural gas (MiQ certification), and an incredibly negative -4.09 to -10.40 kg CO₂e/kg H₂ when fed with Renewable Natural Gas (RNG).

Energy sustainability and emission intensity

Energy sustainability in the context of hydrogen transcends mere emission reduction to encompass four critical dimensions: life-cycle carbon intensity, process energy efficiency, resource availability, and transition equity.

A sustainable energy system must operate within planetary boundaries while ensuring universal and affordable access. For clean hydrogen, this means it is not enough to be “green” at the point of production; we must consider embodied emissions in the manufacturing of electrolyzers, solar panels, wind turbines, and the entire transport and storage infrastructure.

The Paris Agreement and its emphasis at COP26 established the need for technological solutions to decarbonize fossil-dependent sectors. The UN’s Net Zero Banking Alliance adds financial pressure: credit is now contingent on investor commitment to climate goals for every financed project.

In this framework, clean hydrogen must compete not only on cost but on its actual contribution to decarbonization. Life Cycle Analysis (LCA) studies show that even renewable energies are not entirely zero-carbon: biomass can vary from -48 to +76 kg CO₂e/kg H₂ depending on the source; geothermal, hydroelectric, and offshore wind maintain minimums of 0.26–2.7 kg CO₂e/kg H₂ due to embodied emissions.

Global certification thresholds

Global certification schemes vary dramatically in their emission thresholds, creating a fragmented landscape that complicates international hydrogen trade. The Green Hydrogen Organization imposes the strictest standard: <1.0 kg CO₂e/kg H₂, achievable only by renewables and, in extreme minimal cases, nuclear. The European Union at 3.38 kg CO₂e/kg H₂ aligns with Japan (3.4 kg), while South Korea allows up to 4.0 kg. The China Hydrogen Alliance is the most liberal at 4.9 kg CO₂e/kg H₂.

Organization/Country	Threshold (kg CO2​e/kg H2​)	Strictness
Green Hydrogen Org.	< 1.0	Very High
European Union	≤3.38	High
USA (IRA §45V)	≤4.0	Medium-High
China Hydrogen Alliance	≤4.9	Medium

Oil refining and ammonia production

Replacing gray hydrogen with clean hydrogen in existing applications (primarily refining and the chemical sector, specifically ammonia) is a short-term priority. These sectors present relatively low technical challenges, as they involve a substitution under comparable conditions without a full fuel switch. Currently, hydrogen production for these applications emits 1,100–1,250 Mt CO₂e (including upstream and midstream fossil supply).

Industrial demand for clean hydrogen has tripled, reaching ~95 million tonnes per year globally. The refining sector uses hydrogen for hydrocracking and fuel hydrotreating; the ammonia (fertilizer) industry requires 3/17 of its mass as hydrogen due to stoichiometry (Haber-Bosch). IEA 2050 Net Zero projections suggest 229 Mt/year of NH₃, translating to ~40–45 Mt/year of clean hydrogen for ammonia alone.

Heavy transport: Aviation, maritime, and rail

Hydrogen could help decarbonize hard-to-electrify heavy mobility sectors: shipping, rail, and buses. The IEA’s Global Hydrogen Review 2022 noted progress: the first fleet of fuel-cell trains began operation in Germany, marking a milestone in zero-emission rail. There is strong interest from the maritime sector, with over 100 pilot projects using hydrogen or its derivatives (ammonia, methanol) as fuel.

Hydrogen aviation achieved critical milestones in 2024: Airbus’s ZeroE prototype completed its first flight using fuel cells and advanced propulsion systems. Researchers developed lightweight hydrogen tanks optimized for aircraft, reducing total weight and improving efficiency. However, the economics remain challenging: the cost of green hydrogen at $3–$5/kg (current) vs. jet fuel at ~$1/kg creates a significant competitiveness gap.

Process innovation: Turquoise and biohydrogen

Beyond green and blue, emerging pathways could disrupt the landscape. As mentioned, turquoise hydrogen via pyrolysis demonstrated costs of $0.73/kg in Korea in 2025, making it competitive even against gray hydrogen. Companies such as C-Zero, Monolith Materials (operating a plant in Nebraska producing ~38 t/day of carbon black), BASF, and Huntsman are piloting methane pyrolysis. Graphitic Energy launched a pilot project in Texas producing 1 t/day of solid carbon and hundreds of kg/day of low-carbon hydrogen, operating through the end of 2025.

The challenge for turquoise hydrogen is a scale mismatch: every tonne of H₂ produces ~3 tonnes of solid carbon. The graphite market is ~1.6 million t/year ($7 billion, growing to 2.5 Mt/year by 2030), while global hydrogen demand is ~100 million t/year. “If you want to serve hydrogen demand, you end up with too much carbon. If you want to serve carbon demand, you don’t end up with much hydrogen,” explains Anthony Schiavo (Lux Research). Solutions include permanent carbon storage (landfills where it will not oxidize into CO₂), use in carbon fiber, graphite for Li-ion batteries (projected demand $>4,300$ GWh/year by 2030, 5x vs. 2023), or carbon black for tires ($19$ Mt/year market, $27 billion).

Biohydrogen from biomass (gasification of corn stover, forestry residues) with or without CCS offers pathways with carbon intensities from 0.26 kg CO₂e/kg H₂ (with CCS) to negative values if the biomass captures atmospheric CO₂ and is then geologically sequestered.

PRISMA methodology analyzed over 25,000 publications from 2017–2024 regarding clean hydrogen production, identifying innovations in thermochemical and biological conversion of biomass and organic waste. These routes align with global decarbonization goals, reducing emissions in hard-to-abate sectors like steel and aviation, though they face challenges regarding feedstock sustainability and competition with food/forestry uses.

Conclusions

The adoption of sustainable energy through clean hydrogen is no longer a futuristic vision, but a technical and economic reality that positions hydrogen as a strategic pillar for industrial decarbonization.

The green, blue, and turquoise pathways are advancing toward cost-competitiveness, each offering geographic advantages and specific applications. Emission intensity (kg CO₂e/kg H₂) has become the key metric for accessing markets and incentives, with industries such as steel, refining, ammonia, and heavy transport leading the charge.

Achieving a competitive green LCOH and a Net Zero 2050 future requires a diversified portfolio that combines technological innovation, accessible renewable electricity, and robust incentive policies, leveraging regional resources, existing infrastructure, and industrial capabilities.

References

1. https://climateaction.unfccc.int/Initiatives
2. https://www.anl.gov