By Runeel Daliah, Lux Research
Hydrogen and hydrogen-based fuels will very soon need to fill the gaps where electricity cannot easily or economically replace fossil fuels. This will mean using hydrogen in the transport sector, say for ships and planes, as well as in energy-intensive industries like steel and chemicals.
However, despite a growing appetite for hydrogen, more than 95% of the roughly 120 million metric tons (MT) of hydrogen produced in 2019 came from fossil fuel sources such as natural gas and coal, commonly known as grey and brown hydrogen. In the global hydrogen market, the amount of green hydrogen derived from renewable energy remains a drop in the ocean.
The main reason for this is the sky-high cost of production. Green hydrogen therefore needs to be more cost-competitive to help the industrial sector reduce reliance on fossil fuels for both energy and feedstock. This article will describe two ways to drive down the cost of green hydrogen.
Balancing different formulas
Generating green hydrogen through water electrolysis involves the decomposition of a water molecule into hydrogen and oxygen gases using electricity from renewable resources. When a direct current (DC) power source connecting two electrodes is immersed in either pure water or an electrolyte, hydrogen forms at the cathode while oxygen forms at the anode.
Current configurations of water electrolysis are categorised as alkaline electrolysis cell (AEC), polymer electrolyte membrane electrolysis cell (PEMEC), and solid oxide electrolysis cell (SOEC). These electrolyser units can be deployed in standalone facilities or integrated into refineries and chemical plants where hydrogen is in constant demand.
- AEC is mature and already commercially deployed. The advantages of AEC are durability and relatively low system costs due to the absence of noble metal electrocatalysts. However, the technology also suffers from low current density and poor dynamic operations, which limits the use of AEC with intermittent renewable sources.
- PEMEC is less mature than AEC and is currently only deployed on a small scale. The technology has high current density and operates well with flexible power loads, which is advantageous for renewable energy sources. However, PEMEC technology uses platinum electrocatalysts, resulting in high system costs. An electrocatalyst is a catalyst which can be used for electrochemical reactions to increase the rate of the reaction.
- SOEC is the least developed electrolysis technology and is deployed only on a laboratory scale. Unlike the other two electrolyser units, SOEC operates at high temperatures ranging from around 650–900°C, and water enters the system as steam. The efficiency of SOEC technology is higher than that of AEC and PEMEC by up to 25%, but the technology currently has a low lifetime due to severe material degradation because of the high operating temperatures involved.
Making green energy affordable
There are two approaches to bring down the cost of green hydrogen: technological improvements and cheaper renewable electricity. In the following graph, current and projected costs for green hydrogen production are shown in comparison to natural gas steam methane reforming (SMR).
SMR is a process where methane from natural gas is heated with steam, usually with a catalyst, to produce a mixture of carbon monoxide and hydrogen. In energy, SMR is the most widely used process for the generation of hydrogen.