First of all, "liquid oxygen" is NOT an option. Chemical oxygen (most likely, most common) or Gaseous Oxygen (not likely, due to weight and maintenance considerations)
Secondly. Yes, the cockpit oxygen separate from the passengers, however those Bottle(s) (gaseous) are located IN the E and E compartment. NOT the cockpit. Regulatory requirements are for 30 minutes per flight crew member and any jumpseater on deck.
So theoretically, it could be expected a single individual ONLY using cockpit crew oxygen can last ONLY for 90 to 100 minutes or maybe a little bit more.
Boeing does NOT list portable oxygen bottles in the cockpit as part of their emergency equipment. Most likely portable oxygen bottles NOT in the cockpit. However, I will give that a local (Malaysia) regulatory agency "might" require a single bottle, but not likely.
Exactly how many portable oxygen bottles in the cabin, of course would be known to the airline. For our purposes, Boeing lists only 4 with an additional 15 more as an option.
I will try one more time. A single pilot on cockpit oxygen at best can last 100 to 120 minutes on cockpit oxygen. At 25,000 feet for that period of time, he is either dead OR he has turned the packs back on and is using cabin air. If he has kept the pack off, and a flight attendant gets to at least 1 bottle immediately, they can survive for 1 hour per bottle. Thus outlasting the cockpit crewmember.
I hope you're not seriously suggesting the cockpit O2 is chemically generated, like the pax system. That's a non-starter.
I said "cockpit oxygen" meaning the O2 supply for the cockpit crewmembers, not that the ship's O2 system supply bottles (whether gas or liquid) had to literally be in the cockpit.
30 minutes O2 per crewmember? In a 777 certified for ETOPS? So what do they do when there's smoke or fumes and they're 3 hours from the nearest alternate? Hold their breath, or breath the smoke/fumes? Ditch?
Here is the kicker . . . The oxgen bottle in the cockpit only lasts 30 minutes. Or thats what we plan on. Of course many factors determine the exact amount. Probably longer. But by regulations at least 30 minutes.
These are US FARs, but it's a safe bet ETOPS certified MH 777's could at least meet the following requirements.
(a) General. When operating a turbine engine powered airplane with a pressurized cabin, the certificate holder shall furnish oxygen and dispensing equipment to comply with paragraphs (b) through (e) of this section in the event of cabin pressurization failure.
(b) Crewmembers. When operating at flight altitudes above 10,000 feet, the certificate holder shall supply enough oxygen to comply with §121.329, but not less than a two-hour supply for each flight crewmember on flight deck duty. The required two hours supply is that quantity of oxygen necessary for a constant rate of descent from the airplane's maximum certificated operating altitude to 10,000 feet in ten minutes and followed by 110 minutes at 10,000 feet. The oxygen required in the event of cabin pressurization failure by §121.337 may be included in determining the supply required for flight crewmembers on flight deck duty.