Green hydrogen has been identified as an essential resource of our future energy economy. While compact burner designs with high thermal load density are widely used in industrial and domestic applications, the unique combustion characteristics of hydrogen present fundamental challenges for the design and operation of such burners. The overall goal of this research project is the development of design principles for mesoscale burner arrays operating with hydrogen and its blends with methane, simultaneously featuring high power-density, fuel flexibility, and low pollutant emission. To that end, a fundamental understanding of the interdependencies between nozzle topology and flame characteristics is required, both for single-nozzles and multi-nozzle arrays. In this context, additive manufacturing (AM) opens wide-ranging possibilities, enabling innovative designs. First, design principles for single-nozzles are derived, investigated, and evaluated. Starting from reference geometries, topology manipulations and design patterns are introduced, and investigated through simulations. Resulting nozzles feature integrated structures for optimal flow control, inner-nozzle mixing, and cooling, while maintaining a compact burner layout. Prototypes are realized by powder-bed-based AM. An initial evaluation focuses on flame stability and fuel flexibility. Favorable designs are further investigated using optical techniques, including high-speed chemiluminescence and planar laser-induced fluorescence for the characterization of flame topology and heat release, Raman and IR-emission spectroscopy for temperature measurement, and particle image velocimetry for the determination of flow fields. The nozzle surface temperature is measured via an IR-camera after calibration of material properties. Building on this information, in-situ alloying is applied to optimize the base material 316L regarding resistance to high temperature oxidation and hydrogen diffusion. Optical fibers are incorporated into the burner, initially for the detection of critical operation modes, and later on for an integration of optical diagnostics facilitating measurements at locations typically inaccessible without AM. For optimized nozzles, additional inlet ports are introduced to exploit partial premixing for enhanced fuel flexibility and power density. Concluding the first funding period, flame-flame interactions between adjacent nozzles are investigated aiming for further improvements of the burner performance. Based on these insights, multi-nozzle designs will be investigated in the second funding period. A modular design is foreseen, where the number of nozzles may be adjusted to the maximum power desired and a large power modulation range can be realized. Co-operations with various working groups of the PP have been agreed upon regarding methodological developments in simulation, optical diagnostics, and AM.