- Black hydrogen refers to hydrogen gas (H₂) produced from coal—specifically through a process known as coal gasification. It is considered one of the most carbon-intensive forms of hydrogen production and stands in stark contrast to low-carbon alternatives like green or pink hydrogen. Black hydrogen is sometimes grouped together with brown hydrogen, which is derived from lignite, a lower-grade type of coal, though in some classifications the two are distinct based on the specific coal feedstock used.
- In the coal gasification process, coal is heated to high temperatures in the presence of oxygen and steam, producing a mixture of gases known as syngas, which includes hydrogen (H₂), carbon monoxide (CO), carbon dioxide (CO₂), and other trace gases. The hydrogen is then separated from this gas mixture. The chemical reaction can be simplified as:
- C (coal) + H₂O (steam) → CO + H₂
- Further processing through the water-gas shift reaction can increase the hydrogen yield:
- CO + H₂O → CO₂ + H₂
- The main drawback of black hydrogen lies in its environmental impact. The process releases a significant amount of carbon dioxide, a greenhouse gas that contributes to climate change. Without carbon capture and storage (CCS) technologies, the CO₂ emissions from black hydrogen production are substantial. For this reason, black hydrogen is often cited as one of the dirtiest hydrogen types in terms of carbon footprint, and its widespread use is inconsistent with global decarbonization goals.
- Economically, black hydrogen may appear attractive in countries with abundant coal reserves and established coal infrastructure, such as China, India, and South Africa. In the past, it was considered a viable option for large-scale hydrogen production due to the low cost of coal and the maturity of gasification technology. However, the increasing pressure to reduce emissions and transition away from coal-fired industries has put black hydrogen under intense scrutiny.
- There is ongoing research into combining coal gasification with carbon capture and utilization or storage (CCUS), which could convert black hydrogen into blue hydrogen, a lower-emission alternative. However, this approach remains costly, energy-intensive, and limited in scale, and it doesn’t fully eliminate the upstream environmental and health impacts associated with coal mining and transport.
- In addition to its environmental consequences, black hydrogen is tied to broader issues related to air pollution, land degradation, and water use. Coal extraction and combustion produce pollutants such as particulate matter, sulfur dioxide (SO₂), and heavy metals, which can harm ecosystems and human health.
