One of the easiest ways to separate oxygen from nitrogen is to cool it down. Oxygen will condense at around 90K, while nitrogen will stay gaseous until 77K. You

One of the easiest ways to separate oxygen from nitrogen is to cool it down. Oxygen will condense at around 90K, while nitrogen will stay gaseous until 77K. You need some fairly serious energy input to do this, but it'll be safer than doing electrolysis.