Grey Hydrogen is the most widely produced form of hydrogen globally, accounting for nearly 95% of current hydrogen supply. It is generated using fossil-fuel-based processes—primarily Steam Methane Reforming (SMR) of natural gas and, in some regions, coal gasification.
While Grey Hydrogen is cost-effective and scalable, it releases carbon dioxide directly into the atmosphere, making it the least environmentally sustainable hydrogen category. Despite this, it remains critical for industrial continuity across refining, fertilizers, chemicals, metallurgy, and energy sectors.
Production Pathways
1. Steam Methane Reforming (SMR) – Dominant Route
Feedstock: Natural Gas (Methane, CH₄)
CH₄ + H₂O → CO + 3H₂
CO + H₂O → CO₂ + H₂
High hydrogen yield with direct CO₂ emissions. No carbon capture is applied. Thermal efficiency ranges between 65–75%, making SMR the lowest-cost hydrogen production route globally.
2. Coal Gasification (Regional Use)
Coal reacts with oxygen and steam at high temperature to produce syngas (CO + H₂), which is shifted to increase hydrogen output. This pathway produces significantly higher CO₂ emissions and is used mainly in coal-rich regions.
Key Characteristics
Fossil-fuel-based hydrogen without carbon capture
Industrial-grade purity ranging from 95% to 99.999%
Lowest production cost among hydrogen routes
Established infrastructure and mature technology
High lifecycle carbon emissions
Energy Content & Performance
Gravimetric energy density of approximately 33.3 kWh/kg.
Burns cleanly at point of use, emitting only water vapor.
Carbon footprint arises entirely from production stage.
Physical & Chemical Properties
| Property | Value | Significance |
|---|---|---|
| Molecular Formula | H₂ | Simplest molecule |
| Molecular Weight | 2.016 g/mol | Extremely light |
| Density (STP) | 0.0899 kg/m³ | Lightest gas |
| Boiling Point | –252.9°C | Cryogenic storage |
| Auto-Ignition Temp. | ~500°C | Safety planning |
| Flammability Range | 4–75% in air | Wide ignition window |
| Diffusion Rate | Very high | Rapid dispersion |
Supply & Delivery Formats
Compressed gas cylinders (150–300 bar)
Bulk pipeline and tanker supply
High-pressure tube trailers
On-site hydrogen generation (SMR units)
Applications
Oil & Gas: Hydrotreating, hydrocracking, desulfurization
Chemicals & Fertilizers: Ammonia, methanol, hydrogenation
Metallurgy: Metal reduction, annealing, heat treatment
Electronics: Carrier gas, reduction atmospheres
Food Industry: Edible oil hydrogenation
Energy: Hydrogen blending and pilot combustion projects
Safety, Storage & Handling
Highly flammable with invisible flame
Non-toxic but poses asphyxiation risk
Requires leak detection, ventilation, flame arrestors
Stored as compressed gas, cryogenic liquid, or generated on-site
Grey vs Blue vs Green Hydrogen
| Parameter | Grey | Blue | Green |
|---|---|---|---|
| Feedstock | Fossil fuels | Fossil fuels | Renewables |
| CO₂ Emissions | High | Low (captured) | Near zero |
| Cost | Lowest | Medium | Highest |
| Technology | Mature | Mature | Emerging |
| Scalability | Excellent | Good | Developing |
Market Outlook
Grey hydrogen will remain dominant in the short to medium term due to cost and infrastructure advantages. However, increasing carbon pricing and emission regulations are driving gradual transition toward blue and green hydrogen pathways.