Microbial electrosynthesis of valuable chemicals from the reduction of CO2: a review

The present energy demand of the world is increasing but the fossil fuels are gradually depleting. As a result, the need for alternative fuels and energy sources is growing. Fuel cells could be one alternative to address the challenge. The fuel cell can convert CO2 to value-added chemicals. The potential of bio-fuel cells, specifically enzymatic fuel cells and microbial fuel cells, and the importance of immobilization technology in bio-fuel cells are highlighted. The review paper also includes a detailed explanation of the microbial electrosynthesis system to reduce CO2 and the value-added products during microbial electrosynthesis. Future research in bio-electrochemical synthesis for CO2 conversion is expected to prioritize enhancing biocatalyst efficiency, refining reactor design, exploring novel electrode materials, understanding microbial interactions, integrating renewable energy sources, and investigating electrochemical processes for carbon capture and selective CO2 reduction. The challenges and perspectives of bio-electrochemical systems in the application of CO2 conversion are also discussed. Overall, this review paper provides valuable insights into the latest developments and criteria for effective research and implementation in bio-fuel cells, immobilization technology, and microbial electro-synthesis systems.

Towards a Self-Powered Amperometric Glucose Biosensor Based on a Single-Enzyme Biofuel Cell

This paper describes the study of an amperometric glucose biosensor based on an enzymatic biofuel cell consisting of a bioanode and a biocathode modified with the same enzyme-glucose oxidase (GOx). A graphite rod electrode (GRE) was electrochemically modified with a layer of Prussian blue (PB) nanoparticles embedded in a poly(pyrrole-2-carboxylic acid) (PPCA) shell, and an additional layer of PPCA and was used as the cathode. A GRE modified with a nanocomposite composed of poly(1,10-phenanthroline-5,6-dione) (PPD) and gold nanoparticles (AuNPs) entrapped in a PPCA shell was used as an anode. Both electrodes were modified with GOx by covalently bonding the enzyme to the carboxyl groups of PPCA. The developed biosensor exhibited a wide linear range of 0.15-124.00 mM with an R2 of 0.9998 and a sensitivity of 0.16 μA/mM. The limit of detection (LOD) and quantification (LOQ) were found to be 0.07 and 0.23 mM, respectively. The biosensor demonstrated exceptional selectivity to glucose and operational stability throughout 35 days, as well as good reproducibility, repeatability, and anti-interference ability towards common interfering substances. The studies on human serum demonstrate the ability of the newly designed biosensor to determine glucose in complex real samples at clinically relevant concentrations.

Fabrication and characterization of electrically conducting electrochemically synthesized polypyrrole-based enzymatic biofuel cell anode with biocompatible redox mediator vitamin K3

Enzymatic biofuel cells (EBFCs) hold tremendous potential to power biomedical devices, biosensors, and bioelectronics. Unlike conventional toxic batteries, these electrochemical devices are biocompatible, harnessing energy from physiological fluids and producing usable electrical energy. But the commercialization of EBFCs is limited by the low operational stability, limited power output and poor electron transport efficiency of the enzymatic electrodes. In this study, a novel bioanode exhibiting a high electron transfer ability and long-term stability was fabricated. For the preparation of the anode, surfactant-assisted polypyrrole (PPy) was electrochemically co-deposited on a platinum wire with the simultaneous entrapment of vitamin K3 (VK3) and GOx (glucose oxidase) in the PPy matrix. Herein, conducting PPy acts as an electron transfer enhancer and provides appropriate electrical communication between the active site of the enzyme glucose oxidase (GOx) and the electrode surface. Biocompatible redox mediator vitamin K3 was employed as an electron transfer mediator to shuttle electrons between the oxidized fuel glucose and surface of the electrode in the electrochemical cell. The electrical conductivity of PPy was measured using the four-probe technique of conductivity measurement of semiconductors. The morphological characterization of as-synthesized anode (PPy/CTAB/VK3/GOx) was performed by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrochemical characterization was studied by cyclic voltammetry (CV), linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) techniques. It was observed that the room-temperature conductivity of PPy lies in the semiconducting range and it also shows good stability on exposure to laboratory air, making it a promising material to provide electrical contact. The study developed a bioanode producing a modest current density of 6.35 mA cm-2 in 20 mM glucose solution. The stability, current output and ease of manufacturing process of the electrode make it particularly suitable for employment in biofuel cell applications.

Research Progress in Enzyme Biofuel Cells Modified Using Nanomaterials and Their Implementation as Self-Powered Sensors

Enzyme biofuel cells (EBFCs) can convert chemical or biochemical energy in fuel into electrical energy, and therefore have received widespread attention. EBFCs have advantages that traditional fuel cells cannot match, such as a wide range of fuel sources, environmental friendliness, and mild reaction conditions. At present, research on EBFCs mainly focuses on two aspects: one is the use of nanomaterials with excellent properties to construct high-performance EBFCs, and the other is self-powered sensors based on EBFCs. This article reviews the applied nanomaterials based on the working principle of EBFCs, analyzes the design ideas of self-powered sensors based on enzyme biofuel cells, and looks forward to their future research directions and application prospects. This article also points out the key properties of nanomaterials in EBFCs, such as electronic conductivity, biocompatibility, and catalytic activity. And the research on EBFCs is classified according to different research goals, such as improving battery efficiency, expanding the fuel range, and achieving self-powered sensors.

Fully Autonomous Active Self-Powered Point-of-Care Devices: The Challenges and Opportunities

Quick and effective point-of-care (POC) devices have the chance to revolutionize healthcare in developed and developing countries since they can operate anywhere the patient is, with the possibility of obtaining and sending the results to the doctor without delay. In recent years, significant efforts have focused on developing new POC systems that can screen for biomarkers continuously and non-invasively in body fluids to prevent, diagnose, and manage diseases. However, one of the critical challenges left to address is how to power them effectively and sufficiently. In developing countries and rural and remote areas, where there are usually no well-established electricity grids or nearby medical facilities, and using batteries is unreliable or not cost-effective, alternative power sources are the most challenging issue for stand-alone and self-sustained POC devices. Here, we provide an overview of the techniques for used self-powering POC devices, where the sample is used to detect and simultaneously generate energy to power the system. Likewise, this paper introduced the state-of-the-art with a review of different research projects, patents, and commercial products for self-powered POCs from the mid-2010s until present day.

Conductive Polymers and Their Nanocomposites: Application Features in Biosensors and Biofuel Cells

Conductive polymers and their composites are excellent materials for coupling biological materials and electrodes in bioelectrochemical systems. It is assumed that their relevance and introduction to the field of bioelectrochemical devices will only grow due to their tunable conductivity, easy modification, and biocompatibility. This review analyzes the main trends and trends in the development of the methodology for the application of conductive polymers and their use in biosensors and biofuel elements, as well as describes their future prospects. Approaches to the synthesis of such materials and the peculiarities of obtaining their nanocomposites are presented. Special emphasis is placed on the features of the interfaces of such materials with biological objects.

Recent advances in enzymatic biofuel cells enabled by innovative materials and techniques

The past few decades have seen increasingly rapid advances in the field of sustainable energy technologies. As a new bio- and eco-friendly energy source, enzymatic biofuel cells (EBFCs) have garnered significant research interest due to their capacity to power implantable bioelectronics, portable devices, and biosensors by utilizing biomass as fuel under mild circumstances. Nonetheless, numerous obstacles impeded the commercialization of EBFCs, including their relatively modest power output and poor long-term stability of enzymes. To depict the current progress of EBFC and address the challenges it faces, this review traces back the evolution of EBFC and focuses on contemporary advances such as newly emerged multi or single enzyme systems, various porous framework-enzyme composites techniques, and innovative applications. Besides emphasizing current achievements in this field, from our perspective part we also introduced novel electrode and cell design for highly effective EBFC fabrication. We believe this review will assist readers in comprehending the basic research and applications of EBFCs as well as potentially spark interdisciplinary collaboration for addressing the pressing issues in this field.

Optimizing Covalent Immobilization of Glucose Oxidase and Laccase on PV15 Fluoropolymer-Based Bioelectrodes

Enzymatic biofuel cells (EBCs) represent a promising technology for biosensors, biodevices, and sustainable green energy applications, thanks to enzymes' high specificity and catalytic efficiency. Nevertheless, drawbacks such as limited output power and short lifetime have to be solved. Nowadays, research is addressed to the use of 3D electrode structures, but the high cost and the industrialization difficulties of such electrodes represent a key issue. The purpose of the paper is thus to describe the use of a low-cost commercial conductive polymer (Sigracell^® PV15) as support for the covalent immobilization of glucose oxidase and laccase, for bioanode and biocathode fabrication, respectively. Efficient immobilization protocols were determined for the immobilized enzymes in terms of employed linkers and enzyme concentrations, resulting in significant enzymatic activities for units of area. The analysis focuses specifically on the optimization of the challenging immobilization of laccase and assessing its stability over time. In particular, an optimum activity of 23 mU/cm² was found by immobilizing 0.18 mg/cm² of laccase, allowing better performances, as for voltage output and electrochemical stability, and a direct electron transfer mechanism to be revealed for the fabricated biocathode. This study thus poses the basis for the viable development of low-cost functional EBC devices for biomedical applications.

Recent advancements in the field of flexible/wearable enzyme fuel cells

This review article focusses on new advances in the field of enzyme fuel cells (EFCs), especially, on flexible materials which can be used to make flexible EFCs for wearable devices, three-dimensional (3D) printed structures to prepare electrodes for EFCs and micro/nano electromechanical structures (MEMS/NEMS) to fabricate micro-EFCs. Particular attention is given to newly developed approaches to obtain efficient electrodes for harvesting energy via EFCs. This review article explains the various attributes of these recently developing technologies and their ability to mitigate the energy requirements of flexible/wearable bioelectronic devices. Besides discussing key milestones achieved, this perspective review article also emphasizes the main hurdles that are currently impeding the realization of flexible/wearable EFCs. We have also emphasized on the major hurdles related to the flexible materials required to fabricate wearable EFCs, suitable 3D printing techniques required, and MEMS and NEMS to fabricate micro-EFCs. In all the recently developed techniques, there are some common issues like stability, low power output, mechanical strength and flexibility. This review article also provides various routes to mitigate these issues. The main aim of this perspective article is to develop curiosity among the researchers of various fields to team up in order to address the huge challenges that restrict the real-world application of flexible/wearable EFCs. Such collaboration is important to harness the full potential of EFCs. It is requested to read this review article with supporting information to get the complete essence.

Engineering Self-Powered Electrochemical Sensors Using Analyzed Liquid Sample as the Sole Energy Source

Many healthcare and environmental monitoring devices use electrochemical techniques to detect and quantify analytes. With sensors progressively becoming smaller-particularly in point-of-care (POC) devices and wearable platforms-it creates the opportunity to operate them using less energy than their predecessors. In fact, they may require so little power that can be extracted from the analyzed fluids themselves, for example, blood or sweat in case of physiological sensors and sources like river water in the case of environmental monitoring. Self-powered electrochemical sensors (SPES) can generate a response by utilizing the available chemical species in the analyzed liquid sample. Though SPESs generate relatively low power, capable devices can be engineered by combining suitable reactions, miniaturized cell designs, and effective sensing approaches for deciphering analyte information. This review details various such sensing and engineering approaches adopted in different categories of SPES systems that solely use the power available in liquid sample for their operation. Specifically, the categories discussed in this review cover enzyme-based systems, battery-based systems, and ion-selective electrode-based systems. The review details the benefits and drawbacks with these approaches, as well as prospects of and challenges to accomplishing them.

Hollow Bioelectrodes Based on Buckypaper Assembly. Application to the Electroenzymatic Reduction of O2

A new concept of hollow electrode based on the assembly of two buckypapers creating a microcavity which contains a biocatalyst is described. To illustrate this innovative concept, hollow bioelectrodes containing 0.16–4 mg bilirubin oxidase in a microcavity were fabricated and applied to electroenzymatic reduction of O2 in aqueous solution. For hemin-modified buckypaper, the bioelectrode shows a direct electron transfer between multi-walled carbon nanotubes and bilirubin oxidase with an onset potential of 0.77 V vs. RHE. The hollow bioelectrodes showed good storage stability in solution with an electroenzymatic activity of 30 and 11% of its initial activity after 3 and 6 months, respectively. The co-entrapment of bilirubin oxidase and 2,2-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) in the microcavity leads to a bioelectrode exhibiting mediated electron transfer. After 23 h of intermittent operation, 5.66 × 10−4 mol of O2 were electroreduced (turnover number of 19,245), the loss of catalytic current being only 54% after 7 days.

Self-Powered Potentiometric Sensors with Memory

Potentiometric sensors induce a spontaneous voltage that indicates ion activity in real time. We present here an advanced self-powered potentiometric sensor with memory. Specifically, the approach allows for one to record a deviation from the analyte's original concentration or determine whether the analyte concentration has surpassed a threshold in a predefined time interval. The sensor achieves this by harvesting energy in a capacitor and preserving it with the help of a diode. While the analyte concentration is allowed to return to an original value following a perturbation over time, this may not influence the sensor readout. To achieve the diode function, the sensor utilizes an additional pair of driving electrodes to move the potentiometric signal to a sufficiently high base voltage that is required for operating the diode placed in series with the capacitor and between the sensing probes. A single voltage measurement across the capacitor at the end of a chosen time interval is sufficient to reveal any altered ion activity occurring during that period. We demonstrate the applicability of the sensor to identify incurred pH changes in a river water sample during an interval of 2 h. This approach is promising for achieving deployable sensors to monitor ion activity relative to a defined threshold during a time interval with minimal electronic components in a self-powered design.

Implication of Wood-Derived Hierarchical Carbon Nanotubes for Micronutrient Delivery and Crop Biofortification

A similarity of metal alloy encapsulation with the micronutrient loading in carbon nanoarchitecture can be fueled by exploring carbon nanocarriers to load micronutrient and controlled delivery for crop biofortification. A wood-derived nanoarchitecture model contains a few-graphene-layer that holds infiltrated alloy nanoparticles. Such wood-driven carbonized framework materials with legions of open porous architectures and minimized-tortuosity units further decorated carbon nanotubes (CNTs), which originate from heat treatment to carbonized wood samples. These wood-derived samples can alleviate micronutrient nanoparticle permeation and delivery to the soil. A rapid heat shock treatment can help in distributing N-C-NiFe metal alloy encapsulation in carbon frameworks uniformly in that case; higher heating and rapid extinction of heat shock have led to formation of good dispersion of nanoparticles. The wood-carbon framework decorated with metal alloys displays promising electrocatalytic features and cyclic stability for hydrogen evolution. Envisaged from this strategy, we obtain enough evidence to form an opinion that a singular heat shock process can even lead to a strategy of faster growth of a wood-carbon network with well-dispersed micronutrient metal salts in porous matrices for high-efficiency delivery to the soil. Having envisaged the formation of ultrafine nanoparticles with a good dispersion profile in the case of transition metals and alloy encapsulation in the carbon network due to the rapid heating and quenching rates, we anticipate that the loading of micronutrients in the wood-derived nanoarchitecture of carbonized wood derived carbon nanotube (CW-CNT), which can offer an application in seed germination and enhance growth rates of crops. The experience of controlled experiments on germination of tomato seeds on a medium containing CW-CNT that can diffuse the seed coat with the promotion of water uptake inside seeds for enhanced germination and growth of tomato seedlings can be further extended to cereal crops.

Development of a new biocathode for a single enzyme biofuel cell fuelled by glucose

In this study, we reported the development of Prussian blue (PB), poly(pyrrole-2-carboxylic acid) (PPCA), and glucose oxidase (GOx) biocomposite modified graphite rod (GR) electrode as a potential biocathode for single enzyme biofuel cell fuelled by glucose. In order to design the biocathode, the GR electrode was coated with a composite of PB particles embedded in the PPCA shell and an additional layer of PPCA by cyclic voltammetry. Meanwhile, GOx molecules were covalently attached to the carboxyl groups of PPCA by an amide bond. The optimal conditions for the biocathode preparation were elaborated experimentally. After optimization, the developed biocathode showed excellent electrocatalytic activity toward the reduction of H₂O₂ formed during GOx catalyzed glucose oxidation at a low potential of 0.1 V vs Ag/AgCl, as well as good electrochemical performance. An electrocatalytic current density of 31.68 ± 2.70 μA/cm² and open-circuit potential (OCP) of 293.34 ± 15.70 mV in O₂-saturated 10 mM glucose solution at pH 6.0 were recorded. A maximal OCP of 430.15 ± 15.10 mV was recorded at 98.86 mM of glucose. In addition, the biocathode showed good operational stability, maintaining 95.53 ± 0.15% of the initial response after 14 days. These results suggest that this simply designed biocathode can be applied to the construction of a glucose-powered single enzyme biofuel cell.