The coupled quantum dynamics of electrons and protons is ubiquitous in many dynamical processes involving light-matter interaction including solar energy conversion in artificial photocatalytic devices and photosynthesis. A first-principles description of such nuclear-electronic quantum dynamics requires not only the time-dependent treatment of nonequilibrium electron dynamics but also that of quantum protons. We discuss new real-time nuclear-electronic orbital time-dependent density functional theory (RT-NEO-TDDFT) approach to study such dynamics in complex extended systems. We apply the new first-principles method to studying coupled quantum dynamics of electrons and protons in complex heterogeneous systems such as semiconductor-molecule interfaces and photoactive molecules in water. Developing the fundamental understanding for such quantum dynamical processes at the atomistic level is central to photocatalytic CO2 reduction, as pursued in the U.S. Department of Energy’s Energy Innovation Hub, Center for Hybrid Approaches in Solar Energy to Liquid Fuels (CHASE) headquartered at the University of North Carolina at Chapel Hill (UNC). Our work articulates how atomistic environments such as hydrogen-bonding water molecules and an extended material surface impact the coupled quantum dynamical process. I will conclude by discussing outstanding challenges and other related method development efforts from my research group at UNC.