Waste heat valorization for hydrogen production: a meta-analytic review of technologies, challenges, and paths to net-zero

Waste heat from industry and renewable energy, in conjunction with appropriate energy conversion processes, exhibit substantial potential as resources for providing thermal energy across diverse applications. The value of waste heat increases when combined with hydrogen production, facilitating significant energy conservation, enhancing energy efficiency, and valorizing the industrial byproducts. Although this concept has the potential to contribute to international decarbonization goals, there remains a lack of extensive analysis of studies on waste heat applications. The purpose of this review is to facilitate integration between academia and industry by analyzing a range of waste heat sources, their contributions to hydrogen production, energy efficiency, and carbon reduction, and their technology maturity level. The meta-analysis of 117 studies demonstrated that a minimum hydrogen production rate of 0.01 kg/h in laboratory-scale PEM systems to a maximum of 1900 kg/h in thermochemical cycles could be achieved. Additionally, about 38% of the studies reported an improvement in energy efficiency between 5% and 15% through the incorporation of waste heat use. Furthermore, the review identified that category 1 sources (engines, turbines, and fuel cells) accounted for most studies, at 52%, followed by category 2 (industrials) at 24%, while integration with category 3 (renewables) had the smallest share, at 19%. This review highlights critical obstacles that hinder the implementation of waste heat integration, such as variations in feedstock, material durability, and inadequate infrastructure, while providing suggestions for future directions, e.g., robust and durable materials, modular hybrid systems, and the potential role of GenAI for reducing costs and promoting commercialization.