Why can hydrogen gas warm up when it expands at room temperature?

When hydrogen gas expands from high to low pressure at room temperature, its temperature rises because the repulsive forces between its molecules exceed the attractive forces.1

In most real gases, expansion causes cooling because energy is consumed to overcome the long-range attractive forces between molecules. However, hydrogen possesses unusually weak intermolecular forces. At room temperature, these attractive forces are insufficient to dominate the interaction, and the prevalence of repulsive forces results in a temperature increase during expansion.21

This behavior is a specific manifestation of the Joule-Thomson effect, which describes the temperature change of a gas during expansion without the production of work or transfer of heat. Hydrogen will only exhibit a cooling effect upon expansion if it is pre-cooled below approximately −68.6° C, the temperature at which attractive forces begin to predominate.231