‘Blue hydrogen’ more carbon-intensive than gas and coal

Hydrogen is a potentially zero-carbon fuel source, producing just heat and water when burned or used in fuel cells and making it an attractive alternative to fossil fuels in transport, heating and industry. For instance, part of the UK government’s decarbonisation plan is a significant expansion in hydrogen to 5GW of capacity by 2030.

There are two approaches to producing hydrogen: blue hydrogen (produced by splitting natural gas into hydrogen and carbon dioxide) and green hydrogen (produced by splitting water via electrolysis into hydrogen and oxygen). While green hydrogen requires a large energy input, blue hydrogen cannot be described as a zero-emission fuel source, though it may be described as net-zero when used in conjunction with efficient carbon capture. Climate think tanks and campaigners have warned the UK government that blue hydrogen expansion will compromise its net-zero target.

The Cornell and Stanford researchers assessed the carbon footprint associated with blue hydrogen as defined by the US Department of Energy. The process begins by converting methane to hydrogen and carbon dioxide using heat, steam and pressure (grey hydrogen). Once some of the carbon dioxide has been captured and sequestered along with other impurities, it can be classed as blue hydrogen. This is a particularly energy-intensive process, with energy typically provided by burning more natural gas.

The researchers calculated that the carbon footprint to create blue hydrogen is more than 20 per cent greater than using either natural gas or coal directly for heat and 60 per cent greater than using diesel oil for heat.

“In the past, no effort was made to capture the carbon dioxide by-product of grey hydrogen and the greenhouse gas emissions have been huge,” said Professor Robert Howarth, a Cornell University environmental biologist. “Now the industry promotes blue hydrogen as a solution, an approach that still uses the methane from natural gas, while attempting to capture the by-product carbon dioxide. Unfortunately, emissions remain very large.”

Methane is a potent greenhouse gas: more than 100 times stronger as an atmospheric warming agent than carbon dioxide when first emitted. The UN’s recent climate change report called on governments to focus on cutting methane emissions in addition to decarbonisation efforts.

Emissions of blue hydrogen are less than for grey hydrogen by nine per cent to 12 per cent. The researchers wrote: “Blue hydrogen is hardly emissions free. Blue hydrogen as a strategy only works to the extent it is possible to store carbon dioxide long-term indefinitely into the future without leakage back to the atmosphere.”

Commenting on indiscriminate political support for hydrogen, Howarth said: “Political forces may not have caught up with the science yet. Even progressive politicians may not understand for what they’re voting. Blue hydrogen sounds good, sounds modern and sounds like a path to our energy future. It is not.”

The researchers emphasised the difference between blue hydrogen and green hydrogen, the latter of which has not yet been commercially realised.

“The best hydrogen, the green hydrogen derived from electrolysis - if used widely and efficiently - can be that path to a sustainable future,” said Howarth. “Blue hydrogen is totally different.”