Hydrogen plays a pivotal role to limit global warming to 1.5 degrees C, offering solutions for sectors such as energy and heavy industry. However, most of the hydrogen production currently depends on fossil fuels, while green hydrogen production faces economic constraints. Bioelectrochemical systems, such as microbial electrolysis cells, offer an alternative route by coupling wastewater treatment with sustainable hydrogen generation. This review critically examines recent advances in bacteria-based cathodes, with a specific focus on purple non-sulfur bacteria as photoelectroactive biocatalysts. Chemical and physical principles governing photo-assisted microbial electrolysis cells are elucidated, including charge transfer mechanisms, energy recovery pathways, and the role of light-driven metabolism in cathodic hydrogen evolution. The performance of purple non-sulfur bacteria-based systems is analyzed under different electrode polarization and illumination conditions, and critically compared with current hydrogen production technologies. Despite demonstrating hydrogen production costs in the range of approximately 1.1-4.5 $ kg-1, photosynthetic bacteria-based electrolysis systems remain at low technology readiness levels (TRL 2-3), reflecting the gap between laboratory validation and industrial deployment. In addition, the most representative wastewater substrates investigated to date are reviewed with respect to process efficiency and scalability. Finally, a future-oriented roadmap is outlined, highlighting key challenges for real-world implementation and the potential of digital tools, artificial intelligence, and digital twin approaches to optimize system control and accelerate the integration of bacteria electrolysis into energy-positive wastewater treatment plants.

A biohybrid microbial anode integrating intact cells of the anoxygenic photosynthetic bacterium Rhodobacter capsulatus (R. caps) with a nanocomposite of histidine-functionalized reduced graphene oxide sheets decorated with gold nanoparticles is reported to tackle inefficient extracellular electron transfer. The nanoengineered biohybrid electrode achieved enhanced current generation while utilizing olive mill wastewater (OMW) as a model waste-derived substrate. The system was benchmarked against a previously developed bioelectrode based on R.caps immobilized in a polydopamine matrix, with the nanoengineered microbial anode demonstrating a 2fold increase in current density (achieving 12.0 +/- 0.6 & micro;A cm- 2) and a 6-fold enhancement in total charge generation under solar light irradiation. The developed biohybrid anode operating in a complete single chamber microbial fuel cell with a 1:1 (v/v) mixture of Lovley and Phillips electrolyte and OMW allowed achieving a power density of 2.1 +/- 0.3 & micro;W cm- 2. The result is attributed to the biohybrid architecture, which reduces charge transfer resistance and enhances faster electron transport kinetics at the bio-nano interface. Overall, this work demonstrates a promising strategy for engineered photoelectrochemical systems aimed at waste valorization and renewable energy conversion.

Copper contamination in the environment poses significant risks to both soil and human health, making the need for reliable monitoring methods crucial. In this study, we report the use of the EmStat Pico module as potentiostat to develop a portable electrochemical biosensor for copper detection, utilizing yeast Saccharomyces cerevisiae cells immobilized on a polydopamine (PDA)-coated screen-printed electrode (SPE). By optimizing the sensor design with a horizontal assembly and the volume reduction in the electrolyte solution, we achieved a 10-fold increase in current density with higher range of copper concentrations (0–300 µM CuSO4) compared to traditional (or previous) vertical dipping setups. Additionally, the use of genetically engineered copper-responsive yeast cells further improved sensor performance, with the recombinant strain showing a 1.7-fold increase in current density over the wild-type strain. The biosensor demonstrated excellent reproducibility (R2 > 0.95) and linearity over a broad range of copper concentrations, making it suitable for precise quantitative analysis. To further enhance portability and usability, a Bluetooth-enabled electrochemical platform was integrated with a web application for real-time data analysis, enabling on-site monitoring and providing a reliable, cost-effective tool for copper detection in real world settings. This system offers a promising solution for addressing the growing need for efficient environmental monitoring, especially in agriculture.

The urgent need for cost-effective and reliable environmental monitoring systems has sparked interest in developing innovative biosensing platforms. Among these, microbial photoelectrochemical biosensors, which leverage the unique properties of photosynthetic microorganisms, have emerged as promising tools for environmental analysis. This perspective examines recent advances in microbial photoelectrochemical biosensor technology, focusing on the fundamental mechanisms of photosynthetic organisms and their integration with materials science. The current limitations in the implementation of microbial photoelectrochemical biosensors will be discussed, highlighting emerging solutions through nanomaterial integration and exploring how these biological systems can be engineered to detect environmental pollutants. Accordingly, a roadmap to transform these biological systems into practical environmental monitoring tools is presented, paving the way to unprecedented opportunities for the development of sustainable, sensitive, and targeted microbial biosensing platforms for real-world pollutant detection. To fully utilize the promise of these next-generation biosensing platforms, future research should concentrate on enhancing signal transduction and its stability over time, optimizing biointerface engineering, and encouraging interdisciplinary collaboration.

Electrodes functionalised with weak electroactive microorganisms offer a viable alternative to conventional chemical sensors for detecting priority pollutants in bioremediation processes. Biofilm-based biosensors have been proposed for this purpose. However, biofilm formation and maturation require 24-48 h, and the microstructure and coverage of the electrode surface cannot be controlled, leading to poorly reproducible signal and sensitivity. Alternatively, semiconductive biocompatible coatings can be used for viable cell immobilization, achieving reproducible coverage and resulting in a stable biosensor response. In this work, we use a polydopamine (PDA)-based coating to immobilize Saccharomyces cerevisiae yeast viable cells on carbon screen printed electrodes (SPE) for Cu(II) detection, with potassium ferricyanide (K3[Fe (CN)6]) as a redox mediator. Under these conditions, the current output correlates with Cu (II) concentration, reaching a limit of detection of 2.2 mu M, as calculated from the chronoamperometric response. The bioelectrochemical results are supported by standard viability assays, microscopy, and electrochemical impedance spectroscopy. The PDA coatings can be functionalised with different mutant strains, thus expanding the toolbox for biosensor design in bioremediation.

The development of ceria (CeO2−x)-based nanoantioxidants requires fine-tuning of structural and surface properties for enhancing antioxidant behavior in biological environments. In this contest, here ultrasmall water-dispersible CeO2−x nanoparticles (NPs), characterized by a high Ce3+/Ce4+ ratio, were synthesized in a non-polar solvent and phase-transfer to an aqueous environment through ligand-exchange reactions using citric acid (CeO2−x@Cit) and post-treatment with dopamine hydrochloride (CeO2−x@Dopa). The concept behind this work is to enhance via surface engineering the intrinsic antioxidant properties of CeO2−x NPs. For this purpose, thanks to electron transfer reactions between dopamine and CeO2−x, the CeO2−x@Dopa was obtained, characterized by increased surface Ce3+ sites and surface functionalized with polydopamine bearing o-quinone structures as demonstrated by complementary spectroscopic (UV–vis, FT-IR, and XPS) characterizations. To test the antioxidant properties of CeO2−x NPs, the scavenging activity before and after dopamine treatment against artificial radical 1,1-diphenyl-2-picrylhydrazyl (DPPH·) and the ability to reduce the reactive oxygen species in Diencephalic Immortalized Type Neural Cell line 1 were evaluated. CeO2−x@Dopa demonstrated less efficiency in DPPH· scavenging (%radical scavenging activity 13% versus 42% for CeO2−x@Cit before dopamine treatment at 33 μM DPPH· and 0.13 mg/mL loading of NPs), while it markedly reduced intracellular ROS levels (ROS production 35% compared to 66% of CeO2−x@Cit before dopamine treatment with respect to control—p < 0.001 and p < 0.01, respectively). While steric hindrance from the dopamine-derived polymer layer limited direct electron transfer from CeO2−x NP surface to DPPH·, within cells the presence of o-quinone groups contributed with CeO2−x NPs to break the autoxidation chain of organic substrates, enhancing the antioxidant activity. The functionalization of NPs with o-quinone structures represents a valuable approach to increase the inherent antioxidant properties of CeO2−x NPs, enhancing their effectiveness in biological systems by promoting additional redox pathways.

The low-cost and early monitoring of metal ion contaminants is paramount to prevent widespread contamination of water environments. Self-powered microbial electrochemical sensors represent an interesting approach to achieving this goal. Purple non-sulfur bacteria have a versatile metabolism and a well-characterized photosynthetic system, making them an ideal candidate for developing biohybrid technologies. In this work, we report the use of these bacteria in biophotoelectrodes to develop self-powered monitoring systems for two common pollutants, NiCl2 and CuSO4. The microbial biophotoelectrode was obtained on a homemade poly-hydroxybutyrate-carbon nanofibers electrode modified with a redox-adhesive polydopamine matrix-based entrapping the purple bacterium Rhodobacter capsulatus. The presence of 500 μM NiCl2 resulted in a 60 % decrease in current density, while the simultaneous presence of 100 μM NiCl2 and 100 mM CuSO4 led to an 83 % current inhibition. Given the implementation of the biophotoelectrode in the field, the biohybrid system was tested in a complex matrix containing beer, demonstrating the promising ability of the photoelectrochemical system to act as an efficient biosensor in complex solutions. Finally, the biohybrid electrode was coupled to a cathode performing oxygen reduction, which allowed obtaining a self-powered monitoring system, paving the way for the future implementation of a low-cost monitoring system for widespread metal ions contaminant monitoring.

The development of bioelectrochemical systems requires careful selection of both their biotic and abiotic components to obtain sustainable devices. Herein, we report a biophotoelectrode obtained with polyhydroxybutyrate (PHB), a biopolymer, which purple non-sulphur bacteria produce as an energy stock under specific environmental conditions. The electrode was obtained by casting a mixture composed of PHB and carbon fibers in a 3:2 mass ratio. Following, the composite material was modified with polydopamine and thermally treated to obtain a hydrophilic electrode with improved electrochemical behavior. The bio-based electrode was tested with metabolically active cells of Rhodobacter capsulatus embedded in a biohybrid matrix of polydopamine. The system achieved enhanced catalytic activity under illumination, with an 18-fold increase in photocurrent production compared to biophotoelectrodes based on glassy carbon, reaching a current density of 12 ± 3 μ A cm −2 , after 30 min of light exposure at +0.32 V. The presented biocompatible electrode provides a sustainable alternative to metal-based and critical raw material-based electrodes for bioelectrochemical systems.

The coupling of biological organisms with electrodes enables the development of sustainable, low cost, and potentially self-sustained biosensors. A critical aspect is to obtain portable bioelectrodes where the biological material is immobilized on the electrode surface to be utilized on demand. Herein, we developed an approach for the rapid entrapment and immobilization of metabolically active yeast cells in a biocompatible polydopamine layer, which does not require a separate and time-consuming synthesis. The reported approach allows obtaining the "electrical wire" of intact and active yeast cells with resulting current generation from glucose oxidation. Additionally, the electrochemical performance of the biohybrid yeast-based system has been characterized in the presence of CuSO4, a widely used pesticide, in the environmentally relevant concentration range of 20-100 mu M. The system enabled the rapid preliminary monitoring of the contaminant based on variations in current generation, with a limit of detection of 12.5 mu M CuSO4. The present approach for the facile preparation of portable yeast-based electrochemical biosensors paves the way for the future development of sustainable systems for environmental monitoring.

Strategies of renewable energy production from photosynthetic microorganisms are gaining great scientific interest as ecosustainable alternatives to fossil fuel depletion. Green microalgae have been thoroughly investigated as living components to convert solar energy into photocurrent in biophotovoltaic (BPV) cells. Conversely, the suitability of diatoms in BPV cells has been almost completely unexplored so far, despite being the most abundant class of photosynthetic microorganisms in phytoplankton and of their good adaptability and resistance to harsh environmental conditions, including dehydration, high salinity, nutrient starvation, temperature, or pH changes. Here, we demonstrate the suitability of a series of diatom species (Phaeodactylum tricornutum, Thalassiosira weissflogii, Fistulifera pelliculosa, and Cylindrotheca closterium), to act as biophotoconverters, coating the surface of indium tin oxide photoanodes in a model BPV cell. Effects of light intensity, cell density, total chlorophyll content, and concentration of the electrochemical mediator on photocurrent generation efficiency were investigated. Noteworthily, biophotoanodes coated with T. weissflogii diatoms are still photoactive after 15 days of dehydration and four rewetting cycles, contrary to analogue electrodes coated with the model green microalga Dunaliella tertiolecta. These results provide the first evidence that diatoms are suitable photosynthetic microorganisms for building highly desiccation-resistant biophotoanodes for durable BPV devices.

Recent advances in coupling light-harvesting microorganisms with electronic components have led to a new generation of biohybrid devices based on microbial photocatalysts. These devices are limited by the poorly conductive interface between phototrophs and synthetic materials that inhibit charge transfer. This study focuses on overcoming this bottleneck through the metabolically-driven encapsulation of photosynthetic cells with a bio-inspired conductive polymer. Cells of the purple non sulfur bacterium Rhodobacter sphaeroides were coated with a polydopamine (PDA) nanoparticle layer via the self-polymerization of dopamine under anaerobic conditions. The treated cells show preserved light absorption of the photosynthetic pigments in the presence of dopamine concentrations ranging between 0.05–3.5 mM. The thickness and nanoparticle formation of the membrane-associated PDA matrix were further shown to vary with the dopamine concentrations in this range. Compared to uncoated cells, the encapsulated cells show up to a 20-fold enhancement in transient photocurrent measurements under mediatorless conditions. The biologically synthesized PDA can thus act as a matrix for electronically coupling the light-harvesting metabolisms of cells with conductive surfaces.

Shedding light on the interaction between inorganic nanoparticles (NPs) and living microorganisms is at the basis of the development of biohybrid technologies with improved performance. Au NPs have been shown to be able to improve the extracellular electron transfer (EET) in intact bacterial cells interfaced with an electrode; however, detailed information on the role of NP-surface properties in their interaction with bacterial membranes is still lacking. Herein, we unveil how the surface functionalization of Au NPs influences their interaction with photosynthetic bacteria, focusing on cell morphology, growth kinetics, NPs localization, and electrocatalytic performance. We show that functionalization of Au NPs with cysteine in the zwitterionic form results in a uniform NPs distribution in purple bacteria, specifically locating the NPs within the outer-membrane/periplasmic space of bacterial cells. These biohybrid cells, when coupled with an electrode, exhibit enhanced EET and increased (photo)current generation, paving the way for the future development of rationally designed biohybrid electrochemical systems.

Photosynthetic bacteria are anoxygenic microorganisms with highly versatile metabolism, as they use sunlight to oxidize a broad variety of organic compounds in addition to heterotrophic and photoautotropic alternative metabolisms. Recent advances in coupling light-harvesting microorganisms with electronic components has led to a new generation of biohybrid devices based on microbial photocatalysts. These devices are limited by the poorly conductive interface between phototrophs and synthetic materials that inhibit charge transfer. Polydopamine (PDA), produced by self-assembly of dopamine, is a very versatile and bioinspired polymer with widespread applications 1 mostly due its ability to adhere and cover surfaces of different chemical composition. The oxidative conditions employed for the formation of this dark insoluble polymer are mild and biocompatible and have inspired scientists to develop novel nanomaterials. Post-functionalization of PDA 2 also enables fine tuning of properties. Furthermore, the ability of this monomer to self-assemble and polymerize in the bacterial growth medium was considered one of the requirements of the polymer to be used as coating material beside the tunable conductive properties and the flexible structure. Biocompatibility of dopamine was tested by in vivo addition in the growth media of the photosynthetic purple non sulphur Rhodobacter (R.) sphaeroides 3 in anoxygenic conditions. This study focuses on overcoming the bottleneck of biohybrid devices through the metabolically-driven encapsulation of photosynthetic cells with a bio-inspired conductive polymer. The treated cells show preserved light absorption of the photosynthetic pigments in the presence of dopamine concentrations ranging between 0.05 – 3.5 mM. The thickness and nanoparticle formation of the membrane-associated PDA matrix was further shown to vary with the dopamine concentrations in this range. Compared to uncoated cells, the encapsulated cells show up to a 20-fold enhancement in transient photocurrent measurements under mediatorless conditions. The biologically synthesized PDA can thus act as a matrix for electronically coupling the light-harvesting metabolisms of cells with conductive surfaces. 1 Liu, Y.; Ai, K.; Lu, L. Polydopamine and its derivative materials: Synthesis and promising applications in energy, environmental, and biomedical fields. Chem. Rev. 2014, 114, 5057–5115. 2 Buscemi, G., Vona, D., Ragni, R., Comparelli, R., Trotta, M., Milano, F., Farinola, G.M., Polydopamine/Ethylenediamine Nanoparticles Embedding a Photosynthetic Bacterial Reaction Center for Efficient Photocurrent Generation. Adv. Sustainable Syst. 2021, 2000303. 3 Labarile, R.; Varsalona, M.; Vona, D.; Stufano, P.; Grattieri, M.; Farinola, G. M.; Trotta, M., A novel route for anoxygenic polymerization of dopamine via purple photosynthetic bacteria metabolism. MRS Advances 2023

Dopamine is an efficient building block to produce a versatile coating polymer able to adhere on a vast repertoire of material surfaces. Polydopamine, a dark-bioinspired polymer, is produced by the self-assembly of the dopamine under aerobic conditions in an alkaline environment. The presence of oxygen is crucial for self-polymerization of dopamine in aqueous solution. In this manuscript we show that is possible to drive the polymerization in absence of oxygen exploiting the metabolism of anaerobic photosynthetic purple bacteria. Graphical Abstract

Abstract The outstanding metabolic versatility of purple non‐sulphur bacteria makes these organisms an ideal candidate for developing photobioelectrochemical systems applicable in contaminated environments. Here, the effects of 2,4 dinitrophenol, a common contaminant, on purple bacteria photobioelectrocatalysis were investigated. The aromatic contaminant clearly affects current generation, with an enhanced photocurrent obtained at low dinitrophenol concentrations (0.5–1 μM), while higher values (up to 100 μM) resulted in a gradual decrease of photocurrent. The obtained electrochemical evidence, coupled to spectroscopic studies, allowed verifying the viability of the bacteria cells after exposure to dinitrophenol, and that no alteration of the photosynthetic apparatus was obtained. The results indicate that high dinitrophenol concentrations divert electrons from the extracellular electron pathway to an alternative electron sink. The present results open the door to the possible use of intact bacteria‐based photoelectrodes to develop technologies for sustainable biosensors with simultaneous environmental remediation.

Dedicated to Plamen: In this Guest Editorial, we intend to celebrate the 60th birthday of Prof. Plamen Atanassov. We have here described his personal and scientific journey highlighting the contributions to the field of electrochemistry and in particular to electrocatalysis and bioelectrochemistry. Personal stories of four colleagues or former students/Post Docs of him are reported highlighting the impact of Plamen not just in science but also in the personal life of people. This Special Collection is dedicated to Plamen Atanassov to celebrate his 60th birthday. For all those of you that know Plamen, you are well aware of his passion and devotion to science, technology, and history. Plamen is an excellent example of a scientist who combines enthusiasm with the highest level of energy and contribution. During his scientific career, he has distinguished himself not only for his prolific publication record, but also for the most interdisciplinary and highly collaborative character of all his research related to electrochemistry. Plamen has proven to be a critical leader in electrocatalysis and bioelectrochemistry with many well-recognized breakthroughs that guide the research directions we travel today. All these accomplishments have been possible thanks to a most fortunate combination of diverse technical preparedness, analytical talent, technical inventiveness, and inter-person organizational skill. In this short celebration, we first briefly describe Plamen's scientific history, which starts in a beautiful, culturally rich and fascinating country in the East of Europe (Bulgaria) leading to his current employment at the University of California Irvine. Secondly, the four scientists leading this celebrating initiative will briefly describe personal experiences and anecdotes related to the impact that Plamen, as an “older brother”, mentor, colleague, and friend has brought into our nowadays lives. Plamen's scientific journey, up to the current days, is a quite unique and fascinating adventure. Plamen graduated at the University of Sofia in 1987 specializing in Chemical Physics & Theoretical Chemistry. In 1988, he obtained a specialization in Bioelectrochemistry at the Frumkin Institute of Physical Chemistry and Electrochemistry, Moscow. He then received his PhD in Physical Chemistry/Electrochemistry from the Bulgarian Academy of Sciences where he was a scientist at the Central Laboratory of Electrochemical Power Sources (now Budevski Institute of Electrochemistry & Power Systems). In 1992, Plamen moved to the United States and joined the University of New Mexico (UNM) as Senior Research Associate (1992–1993), and later as Research Assistant Professor (1993–1999) with the Chemical & Nuclear Engineering department. He then left academia to join a startup company named Superior MicroPowders LLC (acquired in 2004 by Cabot Corp.) as Research Scientist. In 2000, he was hired as Assistant Professor with the Chemical & Nuclear Engineering department where in 2006 he became Associate Professor and Full Professor in 2009. He founded the UNM Center for Emerging Energy Technologies (CEET) in 2007, serving as the founding director till 2011. In the period 2012–2013 he was Associate Dean for Research of UNM School of Engineering. In 2014, he became Distinguished Professor of Chemical & Biological Engineering (new department name) at UNM. In 2015, he was appointed Director of the UNM Center for Micro-Engineered Materials (CMEM), a joint laboratory between UNM and Sandia National Laboratories. Plamen spent two sabbatical years, the first one in 2007 as a Visiting Researcher at the Hawaii Natural Energy Institute, University of Hawaii, Manoa, Honolulu, and the second one in 2014 as Visiting Professor at the University of Padua (Padua, Italy); University of Sofia, (Sofia, Bulgaria); University of Grenoble-Alps (Grenoble), and as Total Chair with the University of Montpellier (Montpellier, France). Starting in October 2018, Plamen joined the University of California Irvine (UCI) where he is a Chancellor's Professor with the Department of Chemical & Biomolecular Engineering, holding secondary appointments with Materials Science & Engineering and Chemistry. His educational efforts are directed toward creating a PhD program in Electrochemistry & Electrochemical Engineering. Currently, Plamen is engaged in several major initiatives of the United States Department of Energy, participating in the team to build the California Clean Hydrogen Hub – Alliance for Renewable Clean Hydrogen Energy Systems (ARCHES) and interfacing with hydrogen technology demonstration and research efforts in the Pacific/Mountain/Southwest regions and Nation-wide. Plamen is a bioelectrochemist “by training”, but he has been able to successfully translate this knowledge into other fields such as electrocatalysis for electrochemical devices, focusing mainly on metal air batteries and fuel cells. His bioelectrochemistry achievements span from enzymatic bioelectrochemistry to sensing and glucose biosensing, including long-term implantable glucose monitoring and intravenous monitoring of glucose and lactate, electrochemical immunosensors for viral and bacterial detection and DNA-based sensors. Important breakthroughs are reported for enzymatic oxygen reduction and glucose oxidation, as well as lowest level of bacterial cell detection by hand-held and portable devices. Integration of these reactions into electrodes through proper immobilization has led to paper-based enzymatic fuel cells. Design of efficient gas diffusion electrodes has led to a significant boost in the power output. Similarly, an innovative silica immobilization technique led to bacteria-based cells with well-defined biofilms. He has been one of the pioneers in the recent development and advancement of platinum group metal-free (PGM-free) electrocatalysts. Silica templated synthesis of such transition metal-nitrogen-carbon (M−N−C) materials gave rise to the first commercially available PGM-free catalysts, used currently as a benchmark by many. Plamen pioneered the use of M−N−C catalysts for circum-neutral pH in biological/microbial electrochemical systems. These catalysts have revolutionized the cathode performance in microbial electrochemical technologies and systems for biological and bio-inspired energy harvesting and water treatment. Plamen's materials for energy programs has been focused on development of novel electrocatalysts for which he is one of the main worldwide recognized contributors, with particular attention to non-platinum electrocatalyst for fuel cells, nano-structured platinum catalysts, and advanced supports. Novel materials synthesis and development, along with integration into electrodes, has redrawn the roadmap for future advances, and led to significant technological transfer. Most recently, Plamen's research direction has expanded towards catalysts for CO2 electroreduction and product valorization, electrosynthesis of ammonia and new materials, and enabling technologies for energy conversion and storage. He holds 56 issued US patents, a substantial number of which have been licensed and form the core of commercial catalyst products. He has published more than 450 peer-reviewed papers (bringing 35 K+ citations and forming an h-index of 95). Importantly, he supervised 40 completed PhD dissertations at UNM and UCI and had advised more than 25 postdoctoral fellows. For each PhD graduated, he collects a bottle of different sparkling wine or juice, each with the defense date and signature of the student. His PhD students and post-doctoral associates work around the USA and entire world, and each has a story to tell of growth and achievement. Countless students have benefited from personal and scientific interactions with Plamen, learning from his deep knowledge. These critical scientific achievements have led to national and international recognition. In 2007, he received the ACS Division of Fuel Chemistry Outstanding Service Award. In 2012, he became Honorary Professor of the Budevski Institute of Electrochemistry & Power Systems, Bulgarian Academy of Science. In 2014, he received the STC.UNM Innovation Fellow Award, UNM's highest award for intellectual property and technology transfer. In 2019, he received the Energy Technology Division Research Award from the Electrochemical Society. In 2018 he was inducted in the National Academy of Inventors, and he is now a Fellow of both The Electrochemical Society (2018) and the International Society of Electrochemistry (2020). Plamen served as a Vice-President of the International Society of Electrochemistry (2015–17) and in 2022, he was elected President of the International Society of Electrochemistry (for the 2023–28 term). As an outstanding teacher who regularly receives high praise from students, Plamen is very proud of the “Top Gobbler” ChNE Student Appreciation Award, received from UNM students in 2000 and 2005. We thank all the authors that have submitted and published a contribution to this Special Collection to celebrate the 60th birthday of one of the main contributors of electrocatalysis and bioelectrocatalysis of our time. Happy 60th birthday, Plamen! Our second interaction was at the ECS in Honolulu in 2012 (12/2012) where he organized a Symposium on bioelectrochemistry. Obviously, I avoided presenting my work at this Symposium, organized by Plamen, just to avoid a second “grilling”. However, I had the chance to meet him and propose a possible way of collaborating. He then invited me to spend 10 days at the University of New Mexico (UNM) where I learned how to integrate enzymes at the cathode of a microbial fuel cell. This interaction allowed me to learn many concepts and expand my knowledge, and led to a Becket ECS Summer Fellowship that I spent in his lab. I remember that day in July 2013, waiting outside his office door, and Plamen popping up from behind the corner, dressed in Hawaiian clothes telling me: “Hi Carlo! Welcome home!” Later, I was hired as a Post Doc in his lab and then promoted to Research Professor. I spent four fantastic years with Plamen at UNM, enjoying life and growing very much as person and scientist. Leaving him and the group in 2017 has been a quite challenging and difficult adjustment. Plamen has been very inspiring as person and scientist, and I have noticed that this feeling is shared with many people and not just in the academic context. I remember many group meetings talking about science where I have felt embarrassingly ignorant, but this has given me the possibility to spend night in the library, learn and in turn, grow. I feel that scientifically speaking (and not only), he has been a pillar, and as I have arrived where I am right now and am able to do work I actually love, I need to thank Plamen. He gave me a tremendous opportunity, for which I feel very privileged. I always like to tell my personal story with Plamen as I consider it a story of my personal growth, success, and inspiration. To me, Plamen has been an older brother, a friend, a colleague and a scientific father. I wish him a happy 60th birthday!” I first talked to Plamen on Skype soon after and this conversation changed my life forever. It brought me to United States and opened a completely new career path for me. I started as a post-doc in Plamen's group at University of New Mexico, very different scenery from what my whole life had been to this point. Plamen became my mentor and my friend. He supported me and guided me from the start and continues to do it till this day. I remember a conversation we had right after I became a Research Assistant Professor. He was excited to share with me the good news that I have been promoted and a second later he asked me what I am planning to do next, what is my next career goal. That is Plamen, always thinking ahead, always pushing you to move forward, think big. He convinced me to take on my next adventure and join the team of Orianna Bretschger, which turned to be another big decision in my life. I am where I am and who I am professionally because of Plamen. He gave me the opportunity to touch on so many different scientific topics, learn a lot, grow a lot. Working with him gave me the knowledge and confidence I needed to continue in my career path. I don't know a single topic he is not knowledgeable about, and he is always open and eager to share this knowledge and help. He is always baking new ideas in his head. He is very creative and open minded in both, his professional and personal life. His students love him. At UNM, the students created a board in the lab with our pictures under a sign saying “Plamen slaves” and all of us were so proud and happy to be part of this special group. Plamen, thank you for believing in me and being my professional and personal mentor and a friend. I'm looking forward to many more years of collaboration and friendship. Happy Birthday!” Plamen and I have many research interests in common, spanning bioelectrocatalysis, fuel cells, and electrochemical kinetics. I lean more toward modeling, and Plamen's research has been more rich in physical characterization, and so we have frequently found ways to collaborate, spiced with some healthy competition. All of these interactions have been treasured opportunities to grow our friendship, and get to know Plamen beyond science, as an artist, a storyteller, a teacher, and a father. There are too many fond memories to count, but I′ll bring up this one: I′ve only been to the Great Wall of China once, and it was with Plamen in 2014. I′m a runner and perhaps an athlete, and for the life of me I could not keep up with Plamen as he climbed and descended the staircases of the Great Wall with abandon. To me, that exemplifies the way Plamen approaches life, with an energy and joy that is invigorating and contagious to the rest of us.”

The Front Cover represents how purple bacterial cells utilized in biohybrid electrochemical systems hit, or miss, their “target electrode” with photo-induced electrons depending on the concentration of dinitrophenol at which they are exposed. More information can be found in the Research Article by L. D. de Moura Torquato et al.