Air Tanks for Astronauts

The standard aluminum 80 cubic foot tank on a 40 feet water dive would provide about
45 minutes of breathing time per tank
http://scuba.about.com/od/scuba101/p/How-Long-Does-A-Scuba-Tank-Last.htm

 
25 Scuba tanks for 45 minutes each
1125 min = 18.75 hours 

Scuba Tanks Needed Per Astronaut on Moon EVA - 2 per Back Pack
Apollo	Mission Time	Moon EVA	Minutes	Tanks	Back Packs	Image	Tanks for 2 men
11	08d 03h 18m	02h 31m	151	3.3	1.65 - 2		6.6
12	10d 04h 36m	31h 30m	1890	42.0	21		84.0
14	09d 00h 00m	(2) 09h 25m	565	12.7	6.35		25.4
15	12d 17h 12m	(3) 10h 36m	636	14.1	12		28.2
16	11d 01h 51m	71h 00m (~3 days)	4260	94.7	47.35		189.4
17	12d 13h 52m	(3) 22h 04m	1324	29.3	14.65		58.6

http://www-pao.ksc.nasa.gov/history/apollo/flight-summary.htm

Liquid Oxygen takes up 1/10 of the size at 300 degrees below zero Fahrenheit
Even so, Apollo 16 Astronauts would require 4.735 back packs
What apparatus would heat the frigid liquid oxygen enough to be breathable
at the right temperature - not to hot and not too cold - within seconds?

The back packs of the Astronauts could not hold enough air
as they did not recharge their tanks during the lunar landing.

Boy: "How could astronauts breathe so long on such small air tanks?"