What Is Grey Hydrogen?

One of the most commonly used types of hydrogen is grey hydrogen, a cost-effective yet carbon-intensive form. We explore what grey hydrogen is, how it is produced, its environmental impact, and its role in the energy transition.

What is Grey Hydrogen?

Grey hydrogen refers to hydrogen produced from natural gas or methane through a process called steam methane reforming (SMR). It is the most prevalent form of hydrogen in today’s global energy systems, accounting for the majority of hydrogen production worldwide. While grey hydrogen is affordable and widely available, its production process results in significant carbon dioxide (CO2) emissions, making it a contributor to climate change.

Why is it called Grey Hydrogen?

The term "grey" signifies its carbon-intensive nature. Unlike green hydrogen, which is produced using renewable energy with zero emissions, or blue hydrogen, which captures and stores the emissions, grey hydrogen has no mechanisms in place to mitigate its environmental impact.

How is Grey Hydrogen made?

The steam methane reforming process

Grey hydrogen is primarily produced through steam methane reforming (SMR). This process involves the following steps:

1. Methane reaction with steam: Natural gas (methane) reacts with high-temperature steam under pressure, resulting in hydrogen and carbon monoxide (CO).

2. Water-gas shift reaction: Carbon monoxide reacts with steam to produce additional hydrogen and CO2.

3. Separation: Hydrogen is separated and purified for use in various applications, while the CO2 is typically released into the atmosphere.

Key inputs and outputs

• Inputs: Natural gas, water (as steam), and energy (often derived from fossil fuels).

• Outputs: Hydrogen, carbon dioxide (as a byproduct), and heat.

While the process is efficient in generating hydrogen, it produces approximately 10 kilograms of CO2 for every kilogram of hydrogen.

Environmental impact of Grey Hydrogen

Carbon emissions

Grey hydrogen’s primary environmental drawback is its significant carbon footprint. Globally, the production of grey hydrogen accounts for over 800 million metric tons of CO2 emissions annually, equivalent to the emissions of the aviation industry. This makes it a major contributor to greenhouse gas emissions and a hurdle in achieving climate goals.

Grey Hydrogen and fossil fuel dependency

The reliance on natural gas for grey hydrogen production perpetuates fossil fuel extraction, which carries its own set of environmental risks, including methane leaks and ecosystem degradation.

Why is Grey Hydrogen so common?

Despite its environmental impact, grey hydrogen remains the dominant form of hydrogen for several reasons:

1. Cost-effectiveness:

   • Grey hydrogen is cheaper to produce than its cleaner counterparts, particularly green hydrogen. The infrastructure for SMR is well-established, and natural gas is widely available.

2. Existing infrastructure:

   • Industrial facilities, refineries, and chemical plants are already equipped to produce and use grey hydrogen, reducing the need for significant upfront investment.

3. Global demand:

   • Industries such as ammonia production, oil refining, and methanol synthesis heavily rely on grey hydrogen for their operations.

Challenges of Grey Hydrogen in the energy transition

Carbon intensity

The high CO2 emissions from grey hydrogen production pose a challenge for countries and industries striving to meet net-zero targets. Without capturing and storing emissions, grey hydrogen’s role in a sustainable energy system is limited.

Economic barriers to transition

Switching from grey hydrogen to cleaner alternatives, such as blue or green hydrogen, requires substantial investment in renewable energy, carbon capture technologies, and new infrastructure. This financial barrier slows the adoption of more sustainable hydrogen solutions.

Public and regulatory pressure

Governments, investors, and environmental groups are increasingly pressuring industries to reduce carbon emissions. As policies like carbon pricing and emissions caps gain traction, grey hydrogen may become less economically viable over time.

Grey Hydrogen vs. Cleaner Hydrogen types

Hydrogen is categorised by colours to represent its environmental impact:

Grey Hydrogen

• Production: Steam methane reforming without carbon capture.

• Emissions: High (CO2 released into the atmosphere).

• Cost: Low.

• Applications: Industrial processes, energy generation.

Blue Hydrogen

• Production: Steam methane reforming with carbon capture and storage (CCS).

• Emissions: Moderate (CO2 emissions reduced by CCS).

• Cost: Higher than grey hydrogen but lower than green hydrogen.

• Applications: Similar to grey hydrogen but with a lower carbon footprint.

Green Hydrogen

• Production: Electrolysis powered by renewable energy.

• Emissions: Zero (if powered entirely by renewables).

• Cost: Currently the most expensive option.

• Applications: Energy storage, transportation, and decarbonizing heavy industries.

The future of Grey Hydrogen

Bridging the transition

While grey hydrogen is not sustainable in the long term, it plays a role as a bridge technology in the energy transition. Industries dependent on hydrogen can continue using grey hydrogen while scaling up infrastructure and investments for cleaner alternatives.

Potential for carbon capture integration

Some grey hydrogen facilities may incorporate carbon capture and storage (CCS) technology to reduce emissions, effectively transitioning to blue hydrogen. This intermediate step can help reduce the environmental impact of grey hydrogen without abandoning existing infrastructure.

Shift to Green Hydrogen

As the cost of renewable energy and electrolyser technologies decreases, green hydrogen is expected to replace grey hydrogen in many applications. Governments and industries are investing heavily in green hydrogen to meet sustainability goals.

Grey hydrogen is the most widely used form of hydrogen today, offering cost-effectiveness and scalability but at a significant environmental cost. While its role in the hydrogen economy is essential, the high carbon emissions associated with its production highlight the need for cleaner alternatives. Transitioning to blue and green hydrogen will require substantial investment, policy support, and innovation. However, with the right strategies, grey hydrogen can serve as a stepping stone toward a more sustainable energy future. By understanding its benefits and limitations, industries and policymakers can make informed decisions to balance economic and environmental priorities.