Fossil fuels have been overwhelmingly used in many industry sectors in past decades, causing significant CO₂ and other pollutant emissions, low efficiency, and nonsustainability. Clean and efficient energy storage and conversion via electrochemical reactions associated with hydrogen, oxygen, and water have attracted substantial attention for energy and environmental sustainability. Among compelling energy technologies, hydrogen proton exchange membrane fuel cells (PEMFCs) are a promising zero-emission power source for transportation to mitigate environmental pollution and reduce fossil-fuel dependence. Meanwhile, water electrolyzers have been clearly identified as the sustainable pathway to produce cheap green hydrogen efficiently using renewable electricity. However, current materials, including catalysts, membranes, and ionomers, cannot meet the challenging targets of high-efficiency, low-cost, and long-term durability of hydrogen fuel cells and water electrolyzers. Developing high-performance catalysts from earth-abundant elements to replace current precious metals is crucial for making these hydrogen technologies viable for large-scale clean energy applications. U.S. DOE has continuously supported his research group in the past decade, aiming to address materials issues by designing and scaling up innovative and highly efficient catalysts and electrodes. This talk discusses recent understanding, progress, achievement, and perspective on developing low-cost and high-performance catalysts based on newly emerging atomically dispersed metal-nitrogen-carbon materials for sustainable and clean hydrogen technologies.