ARPA-E Range Extenders for Electric Aviation with Low Carbon, High Efficiency REEACH
DE-FOA-0002240   https://arpa-e-foa.energy.gov/#FoaId2b149083-ee1b-4b74-809f-4256735c8060 

ARPA-E seeks to mitigate the greenhouse gas emissions associated with commercial air travel at minimum economic cost by developing elements of an ultra-high efficient aircraft propulsion system that uses Carbon Neutral Liquid Fuels (CNLFs). Since these fuels generally either have lower specific-energies (kWh/kg) or are projected to have higher cost than traditional fossil-based jet fuels, ultra-high conversion efficiency is critical for the economic viability of this approach. An electrified propulsion system framework postulated by ARPA-E could potentially leverage multiple sources of stored energy (e.g. CNLF, batteries, etc.) to facilitate emerging propulsion concepts (e.g. distributed propulsion) and enable net-zero carbon emissions for long range, narrow-body, commercial aircraft.

The objective of the Range Extenders for Electric Aviation with Low Carbon and High Efficiency (REEACH) program is the development of one element of the electrified propulsion system framework: a system for the conversion of chemical energy contained in energy dense Carbon Neutral Liquid Fuels CNLFs  to electric power for aircraft propulsion and hotel loads.

The development of the all-electric powertrain is the objective of a separate ARPA-E FOA: see Aviation-class Synergistically Cooled Electric-motors with iNtegrated Drives (ASCEND)  https://arpa-e-foa.energy.gov/#FoaId22888746-6728-479a-8b27-f53f97f587a9