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This article conducts a systematic mapping and inductive analysis of existing work related to hydrogen energy policy in the Web of Science Core Collection from 1996 to 7 July 2023. First, based on bibliometrics, the research reveals the publication volume trends, influential contributors (countries, authors, organizations and journals). Second, bibliometric and content analysis were applied to vividly demonstrate the evolution of the research topic, discuss leading research topics, and provide valuable insights into issues that deserving appropriate attention in the future. The unequivocal role of policies in supporting the development of hydrogen energy is undeniable. In the future, the focal point of hydrogen energy policies should be concentrated on stimulating the creation of demand for green hydrogen, necessitating the effective evaluation of policy outcomes and ensuring the safety of hydrogen energy. Furthermore, the application scope of hydrogen energy extends beyond the transportation sector, holding potential for expansion into other high carbon‐emitting domains. With the strengthening of international collaboration in hydrogen energy, considerations of energy justice and fairness are poised to become pivotal factors in cooperation, exerting a profound influence on the attainment of long‐term development and environmental sustainability. These critical research directions will shape the future landscape of hydrogen energy policy and serve as an essential resource for policymakers, researchers, and stakeholders in this domain. [ABSTRACT FROM AUTHOR]

This document is a summary of a special issue of the Journal of Marine Science & Engineering titled "Advanced Research on Sustainable Maritime Transportation." The issue contains 15 research papers that cover various aspects of sustainable maritime transportation, including green shipping technologies, maritime safety, and sustainable port operations. The research papers explore topics such as the challenges of transitioning to low-carbon fuels for maritime diesel engines, fault-tolerant control strategies for electric ships, the impact of emission control areas on ship orders, and the effectiveness of machine learning methods in predicting a ship's carbon intensity index. Other papers focus on maritime security and sustainable port operations, discussing unmanned surface vessels, maritime safety management, and energy-saving solutions for waste heat recovery on ships. The special issue emphasizes the importance of technological innovation and policy adjustment in achieving sustainability goals in the maritime transportation industry. The research presented in these papers provides scientific guidance and practical directions for the industry's sustainable development. [Extracted from the article]

How to evaluate the carbon emission efficiency of multimodal transport is an important issue of public concern, and this article attempts to solve it with a network data envelopment analysis (DEA) model. DEA is a method to evaluate the efficiency of homogeneous decision-making units (DMUs). First, this article studies the efficiency decomposition and efficiency aggregation of the general network structure for DEA model. In efficiency decomposition, the relationship between system efficiency and division efficiency is discussed; whereas in efficiency aggregation, the division tendency brought about by the definition of weights is analyzed. Then, a reasonable and single compromise solution to division efficiency scores is investigated while the system efficiency remains optimal. Finally, a two-stage network DEA model of rail-water intermodal transport is established with carbon dioxide (CO2) emissions as an undesirable output. Based on this model, the rail-water intermodal transport efficiencies of 14 ports in China in 2015 are evaluated by the methods of efficiency decomposition, efficiency aggregation, and non-cooperation. The results show that Rizhao Port, Tangshan Port, Nanjing Port, and Zhuhai Port have set an example to other ports. Qinhuangdao Port, Ningbo-Zhoushan Port, Guangzhou Port, and Beiliang Port need to improve the efficiency of railway transportation. Beibu Gulf port, Zhanjiang Port, Dalian Port, Lianyungang Port, Yantai Port, and Yichang Port should optimize their intermodal system. In addition, Yantai Port and Yichang Port urgently need to improve the port efficiency in low-carbon operation. The network DEA model constructed in this article can be further applied to the efficiency evaluation of multi-link supply chains, and the empirical results can provide a reference for the efficiency evaluation of ports in China. [ABSTRACT FROM AUTHOR]