High specific energy millimeter scale (1-100 We) generators would tremendously unburden the dismounted soldier, revolutionize small autonomous robotic platforms and drones, and enable a proliferation of remote sensors. A thermophotovoltaic (TPV) energy conversion scheme is appealing for millimeter-scale power generators because it is a static process without moving parts or working fluids, has high specific power ultimately limited by the Plank blackbody, and relies on continuous combustion enabling low emissions and multi-fuel operation. Project 3.1 takes a unique approach to TPV based on high temperature photonic crystals, catalytic microcombustion, and low bandgap TPV cells. Researchers have already experimentally demonstrated greater than 4% fuel-to-electricity conversion - a world record for small generators - with a two-dimensional photonic crystal emitter, and predict this approach to be capable of >1000 Wh/kg and >40 W/kg even without additional scientific. The team will perform fundamental investigations (theoretical, numerical, and experimental) of high temperature photonic crystals, as well as develop a robust platform for millimeter-scale hydrocarbon TPV experiments including a developing a microburner. Additionally, the team will explore related applications and technologies, leveraging the microburner design for a thermoelectric power generator, and the TPV platform for radioisotope TPVs. Continued and planned collaborative efforts will take place with colleagues from ARL and the Army’s Natick Soldier Research, Development, and Engineering Center (NSRDEC).