Question:
efficiency of hydrogen production techniques with respect to... a purity of hydrogen produced b energy required per hydrogen mass (negelcting factory construction cost and so on...say, during electrolysis, i just want the electric energy used, not the energy used to create the apparatus, and so on

Answer: It's hard to find a definitive answer for you here. Conventional electrolysis is about 50% efficient (about half the energy splits water molecules and half warms up the water.) A reasonable rate of production along with that efficiency (and a reasonable electrode life expectancy) requires very expensive electrodes. Gases dissolved in the water can be released as well as gases other than hydrogen formed from chemical reactions between the electrolyte and impurities in the water. The hydrogen gas generated also contains water vapor. The hydrogen can be purified relatively easily.

'Reverse' fuel cell type electrolyzers are even more expensive than the good electrolyzer electrodes, but can achieve a practical efficiency of 90% (only 10% of the energy is wasted warming the water.)