The transition to a sustainable, low-carbon energy future requires transformative advancements in energy and environmental technologies. Carbon capture and sequestration, underground hydrogen storage, and nuclear waste geological disposal will be central aspects of a sustainable energy future, which hinge on a hidden world: reactive multiphase flows in opaque, heterogeneous porous media. Despite their foundational importance, the pore-scale dynamics that govern these technologies remain elusive. Here, we argue that microfluidic porous media are emerging as transformative platforms for the direct visualization of multiphase reactive flow in porous media and eventually optimizing these multiple physicochemical and biological processes. This review highlights critical scientific challenges associated with these sustainable energy solutions and summarizes the state-of-the-art microfluidic techniques for studying the interplay between multiphase flow, reactive transport, and biological effects in porous media. We also propose promising microfluidic technologies to support sustainable energy applications further. By offering a comprehensive overview of how microfluidic approaches deepen our understanding of fundamental pore-scale dynamics and connect them to large-scale behavior, this review is expected to promote both experimental and theoretical understanding of multiphase reactive flow in porous media, thereby informing material design, process optimization, and predictive modeling for scalable implementation. By fostering interdisciplinary collaboration across microfluidics, fluid mechanics, geophysics, materials science, and subsurface engineering, we hope to accelerate innovation and advance sustainable energy solutions.