Minimum 2000kj/kg stored when cycling between at T_cold and T_hot.
T_cold not less than 500k
T_hot greater than T_cold but less than 1000k
3atm or less in a closed container. Gas phase is allowed but total density should not be less than 0.5kg/l.
Must be able to cycle at least 10,000 times without losing more than 20% of capacity.
Full bounty will be awarded for identifying a mix of chemicals that satisfies all of these criteria and showing your work to demonstrate it satisfies the criteria. There is no partial credit.
Related questions
not saying this is impossible (it's definitely not! thermochemical energy storage is a well-established concept in literature with decades of precedent) but I'm genuinely rolling at your performance targets here
there are startups that have raised >$10mil Series A to evaluate if they can get to 10,000 cycles going between like 800 <=> 1500 °C at like 1.3~1.8 MJ/kg
"There is no partial credit." LMFAO if anyone reading this thinks they can hit these KPIs, DM me for $500,000 of non-dilutive seed funding
vaporization of phosphorous would be like 3000kj/kg at 553K at 1atm but to get the requisite density of 0.5kg/l you need about 16 mol/l which at that temperature would take about 0.5*22.4*16=179 atms of pressure. Such pressure vessels exist and aren’t that expensive but this violates one of the OP criteria