The present disclosure provides for hydrogen recombiner assemblies utilizing an integrated passive heat sink. More particularly, the present disclosure provides for flameless hydrogen recombiner assemblies utilizing an integrated passive heat sink to convert leaked hydrogen (e.g., inside a spacecraft) to water vapor. In example embodiments, the present disclosure provides for self-regulating and gravity-independent hydrogen recombiner assemblies having an integrated passive heat sink for low-earth orbit (LEO) and deep-space exploration crewed spacecraft, with the hydrogen recombiner assemblies configured to convert leaked hydrogen (e.g., inside a spacecraft) to water vapor.