Key Takeaways & Executive Findings
- •• Comprehensive overview of the evolution of transition metal-based catalysts in microbial electrolysis cells from their inception to the present. • Critical design parameters of catalysts evaluated from technical, economic, and sustainability perspectives. • A conceptual framework is proposed to address current challenges and guide future research based on literature best practices. • The potential of artificial intelligence and advanced computational methods in designing high-performance electrodes is highlighted.
Abstract
Designing high-performance electrocatalysts is one of the key challenges in the development of microbial electrochemical hydrogen production. Transition metal-based (TM-based) electrocatalysts are introduced as an astonishing alternative for future catalysts by addressing several disadvantages, like the high cost and low performance of noble metal and metal-free electrocatalysts, respectively. In this critical review, a comprehensive analysis of the major development of all families of TM-based catalysts from the beginning development of microbial electrolysis cells in the last 15 years is presented. Importantly, pivotal design parameters such as selecting efficient synthesis methods based on the type of material, main criteria during each synthesizing method, and the pros and cons of various procedures are highlighted and compared. Moreover, procedures for tuning and tailoring the structures, advanced strategies to promote active sites, and the potential for implementing novel unexplored TM-based hybrid structures suggested. Furthermore, consideration for large-scale application of TM-based catalysts for future mass production, including life cycle assessment, cost assessment, economic analysis, and recently pilot-scale studies were highlighted. Of great importance, the potential of utilizing artificial intelligence and advanced computational methods such as active learning, microkinetic modeling, and physics-informed machine learning in designing high-performance electrodes in successful practices was elucidated. Finally, a conceptual framework for future studies and remaining challenges on different aspects of TM-based electrocatalysts in microbial electrolysis cells is proposed.
1. Introduction
Innumerable action plans from the beginning of the new century were proposed by the United Nations (UN) on significant issues (like the lack of safe drinking water) to address sustainable solutions for human being. At the forefront of these action plans are the Sustainable Development Goals (SDGs) of the UN Agenda 2030, which are outlined in 17 important Goals for addressing issues in front of human beings and the precious blue planet. In this regard, the scientific communities across different disciplines, from engineering to social science, and even lawmakers have tried to take steps toward these 17 Goals. Of particular interest are Goal 6 and Goal 7, which focus on “Clean Water and Sanitation” and “Clean and Affordable Energy for All” and are considered as two of the most important goals that have multifaceted effects on human beings as well as the environment and a significant impact on realizing other SDGs.
Interestingly, bioelectrochemical systems (BESs) such as microbial fuel cells (MFCs), microbial electrolysis cells (MECs), and microbial electrosynthesis (MESs) in some ways can satisfy both of these goals due to their mechanism which employs wastewater treatment (or CO2) to produce electricity, biohydrogen, and valuable chemicals correspondingly. Interestingly, Sayed et al. studied the interlinkage between SDGs and plant-based BESs and reported that all 17 goals are directly or indirectly realized one or more targets of each SDGs. However, among all BESs they only focused on the MFCs and their interconnection with other SDGs. Moreover, Kathori et al. explicitly highlighted the role of MFC for wastewater treatment and electricity production and its direct relation on realizing of SDG7 and SDG13. Although the link between SDGs and MEC for hydrogen production was not explicitly examined in the literature, a number of researchers showed the substantial role of hydrogen in achieving SDGs. For instance, El-Maroufi et al. showed how the production of green hydrogen through integration of three hybrid renewable energy sources of photovoltaic panels, wind turbines, and biomass generators is considerable step on the realization of the SDG 13. It is important to point out that while wastewater is responsible for heavy pollution of transboundary river throughout the world, it also contains chemical energy.
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Seyed Masoud Parsa, Zhijie Chen, Huu Hao Ngo, Wei Wei, Xinbo Zhang, Ying Liu, Bing-Jie Ni, Wenshan Guo (2025). 15 Years of Progress on Transition Metal-Based Electrocatalysts for Microbial Electrochemical Hydrogen Production: From Nanoscale Design to Macroscale Application. Nano-Micro Letters. https://doi.org/10.1007/s40820-025-01781-6
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Frequently Asked Questions
What are transition metal-based electrocatalysts and why are they important for microbial electrochemical hydrogen production?
Transition metal-based electrocatalysts are materials that facilitate the hydrogen evolution reaction in microbial electrolysis cells (MECs). They are important because they offer a cost-effective and high-performance alternative to noble metal catalysts, which are expensive, and metal-free catalysts, which often have lower efficiency. This review highlights their potential to advance sustainable hydrogen production.
What are the key design parameters for transition metal-based electrocatalysts in MECs?
Key design parameters include the selection of efficient synthesis methods based on material type, criteria during synthesis, and the pros and cons of various procedures. Additionally, strategies for tuning structures, promoting active sites, and exploring novel hybrid structures are critical for optimizing performance.
How do transition metal-based electrocatalysts contribute to the Sustainable Development Goals (SDGs)?
These electrocatalysts enable efficient hydrogen production from wastewater, addressing SDG 6 (Clean Water and Sanitation) and SDG 7 (Affordable and Clean Energy). By treating wastewater and producing clean energy, they also indirectly support other SDGs, such as climate action (SDG 13).
What are the challenges for large-scale application of transition metal-based electrocatalysts?
Challenges include cost assessment, life cycle assessment, and economic analysis. The review also highlights the need for pilot-scale studies and the integration of artificial intelligence and computational methods to design high-performance electrodes for mass production.
What is the significance of artificial intelligence in designing TM-based electrocatalysts?
Artificial intelligence and advanced computational methods, such as active learning, microkinetic modeling, and physics-informed machine learning, can accelerate the discovery and optimization of high-performance electrocatalysts by predicting material properties and guiding experimental efforts, thereby reducing time and cost.
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