• Energy Research

Microbial fuel cell (MFC) has received much attention in the last decade as a promising technology to simultaneously generate electricity and decontaminate wastewater. This study aims to quantitatively review the published literature on MFC, published in the period of 1970–2020, based on the Web of Science (WoS) database. For the first time in literature, a comprehensive quantitative review of MFC has been conducted by employing the technique of bibliometric and content analyses. A total of 11,397 publications have been retrieved from WoS, out of which 81.6% are research articles. The evaluation in the field of MFC has been mapped in various categories, such as publication history, publication distribution, subject category distribution, leading journals, leading countries and leading organizations in MFC research. Additionally, content analysis has been conducted to unearth the research trends in MFC; and some hot research topics in MFC have been spotted. Results depict that the period 2011–2020 has been the most appreciating era for MFC research, as it contributed 87% of the total publications. Among the subject categories, energy fuel and microbiology lead with contributions of 26.5% for each, butthe overall growth of the energy fuel category in the last decade has been the highest. Out of 1,147 journals publishing MFC research, Bioresource Technology is the leading one; and countries like China, USA and India are the main hub of MFC research with 26.47%, 16.95% and 7.69% contributions in publications, respectively. The hottest topics in MFC research are nanoparticles, catalysts, air electrodes, graphene electrodes, power enhancement, air cathode and nitrogen removal. Moreover, major research areas are engineering, energy fuels and biotechnology with each contribution 26.5% of the total publications.

Thermophotovoltaic (TPV) technology harvests electricity from a source of thermal radiation and at current, TPV cells can achieve conversion efficiency of more than 40%. The construct of the TPV system is relatively complex than the conventional solar cell in which the TPV has two critical components, specifically the absorber-emitter and filters, to help in enhancing the transfer of photons to the TPV cell for conversion. Despite its importance, works on the optimization of these components for an ideal TPV system are still lacking. This review examines previous studies on the TPV structure, and details extensive techniques to improve current designs of the TPV systems - notably through the use of textured absorbers, selective emitters and different types of filters. Inevitably, the selection of materials and designs of the absorber-emitter are essential in enhancing the TPV performance. Herein, challenges and enhancements in the form of optical performance, thermal stability, and electrical performance are comprehensively discussed. This review identifies the crucial role of nanoparticles incorporated into the absorber-emitter layer of a TPV system. This review also critically highlights technology advancements incorporated into the TPV technology which will effectively boost performance and improve the fabrication and operational costs of this sustainable technology.