Complex sentence: Later, it was discovered that such excess heat is the result of conventional chemistry, i.e. internal recombination of hydrogen and oxygen, which led to a reduction in the Faraday efficiency of the electrolysis.
Split into simpler sentences: Later, it was discovered that such excess heat can easily be the product of conventional chemistry, i.e. internal recombination of hydrogen and oxygen. Such recombination leads to a reduction in the Faraday efficiency of the electrolysis.