OP's question is actually similar to this one interplanetary trade in around 2400 CE by the nature of the problem.
As a piece of something valuable, even with space scarcity of resources(maybe), I'm glad to present you, the latest invention in energy money - energy diamond.
Scientists are turning nuclear waste into super-efficient diamond batteries
With a half-life of 5,730 years.
A diamond beta-battery containing 1 gram of C14 will deliver 15 Joules per day, and will continue to produce this level of output for 5,730 years — so its total energy storage rating is 2.7 TeraJ.
As energy it has cost about 75'000\$ per gram (0.1\$ per kWh), compare it to the current price of gold \$38,214.73 per kg.
Or it is 75'000'000 per tonne, even with SpaceX ITS prices of projected transporting cost with 140'000 per tonne it worth to transport in physical form if there is such a wish.
- not so easy, in first place because energy in space is cheaper, but best of 3 worlds (energy, matter, and good cutting tool) for those who like physical transfer.
But sure energy does not have to be physically transferred in cases when it is not needed, or impossible to transfer. Same way as gold backed money do not transfer gold.
Purchasing power of energy in different places
- This section is less about having tokens, which OP was asking for, but again more about why energy may be valid as money.
Purchasing power of energy will be different in different places. But to use the energy in a different place one have to deliver that energy to the place, or exchange already present energy in the place to already present energy in another place, if one like to use it there or order something there.
Price for energy from one place will depend on abundance of the energy in that place, abundance of matter in that place, cost of delivering goods and services from/to the place, technologies available, demand for services in the place, offers (what they can do with the energy, and how much other needs what they can do) in the place, energy sources available in different places etc etc.
Purchasing power of energy will define direction from which place to which place this energy is flowing.
If as an example a space station can produce lots of energy for cheap(effort, matter, work hours), but can't produce anything else(for some reason) there are 2 ways to solve the problem
- deliver technologies and/or matter to the space station
- deliver energy to other places where the energy can be actually used to produce useful technologies or products or services.
It works same way as one may have a house in one country, but to actually use it -- one have to be in that house or rent it to others - for money or for services or use the house for other profitable operations.
Same way as currencies, you may have currency of a other country in the country, but one can't directly use that currency to buy something, because they do not accept it as payment, they accept their own currency as payment. They do so because of a reason, artificial and practical reasons. And for those reasons one have to use exchange service to get a currency of the country where he is at the moment, directly or indirectly (as by asking will you accept my money, and they maybe will but how much you money worth they will know from exchange rates of that currency)
Same for energy, one may have Terra Watts of power production on a space station, but if one can't use this energy for something useful it is worthless. If he have to obtain matter and deliver it from Jupiter, to be able to do something with that energy it may be not so much overall.
Also different services will cost different price - on earth recycling is expensive process, because they do not have lot of energy, so they make big trash fields - it is cheaper for them.
On a space station, recycling is cheap, because of cheap energy, but making some kind of trash storage is expensive, because delivery of new materials may be expensive, or just -- worth in energy in the place where it can be obtained and in energy needed to deliver it to the station.
Delivery and gathering the matter from Jupiter will cost about 300kWh/kg (depends on technology you have for gathering), delivery of that matter may cost from Jupiter to some station near earth will cost X amount of matter and energy (depends on technology used in delivery)
In general, it will stimulate matter to flow in a direction where it can be used, energy flow in direction where it can be used, and will stimulate to develop energy efficient technologies.