Efficient, Stable, and Solvent‐Free Synthesized Single‐Atom Catalysts: Carbonized Transition Metal‐Doped ZIF‐8 for the Hydrogen Evolution Reaction**

Abstract Herein we present non‐noble metal single‐atom catalysts (SACs) based on carbonized transition metal‐doped zeolitic imidazolate frameworks (ZIFs) as stable and efficient electrocatalysts for the hydrogen evolution reaction in acidic media. In this work, earth‐abundant metals are embedded in a porous N‐rich carbon matrix by pyrolyzing metal‐doped ZIF structures and characterized by spectroscopic, microscopic, and electrochemical methods. The complete synthesis of these high surface area SACs was carried out without any solvents and hence offers a promising route for a more sustainable catalyst production and industrial upscaling. As the best‐performing catalyst, cobalt SAC illustrated already with a low cobalt loading of <0.3 at.% a substantial increase in activity with an overpotential of −322 mV for −10 mA cm −2 , and high stability during electrolysis at −10 mA cm −2 for 12 h in acidic media, with only a small decrease of 33 mV to more negative potentials after the initiation period.