Abiotic Catalysts Research Articles

Photosynthetic biohybrid systems for solar fuels catalysis.

Photosynthetic reaction center (RC) proteins are finely tuned molecular systems optimized for solar energy conversion. RCs effectively capture and convert sunlight with near unity quantum efficiency utilizing light-induced directional electron transfer through a series of molecular cofactors embedded within the protein core to generate a long-lived charge separated state with a useable electrochemical potential. Of current interest are new strategies that couple RC chemistry to the direct synthesis of energy-rich compounds. This Feature Article highlights recent work from our lab on RC and RC-inspired hybrid systems that capture the Sun's energy and convert it to chemical energy in the form of H2, a carbon-neutral energy source derived from water. Biohybrids made from the Photosystem I (PSI) RC are among the best photocatalytic H2-producing protein hybrids to date. Targeted self-assembly strategies that couple abiotic catalysts to PSI translate to catalyst incorporation at intrinsic PSI sites within thylakoid membranes to achieve complete solar water-splitting systems. RC-inspired biohybrids interface synthetic photosensitizers and molecular catalysts with small proteins to create photocatalytic systems and enable the spectroscopic discernment of the structural features and electron transfer processes that underpin solar-driven proton reduction. In total, these studies showcase the incredible scientific opportunities photosynthetic biohybrid research provides for harnessing the optimal qualities of both artificial and natural photosynthetic systems and developing materials that capture, convert, and store solar energy as a fuel.

Unraveling iron oxides as abiotic catalysts of organic phosphorus recycling in soil and sediment matrices

In biogeochemical phosphorus cycling, iron oxide minerals are acknowledged as strong adsorbents of inorganic and organic phosphorus. Dephosphorylation of organic phosphorus is attributed only to biological processes, but iron oxides could also catalyze this reaction. Evidence of this abiotic catalysis has relied on monitoring products in solution, thereby ignoring iron oxides as both catalysts and adsorbents. Here we apply high-resolution mass spectrometry and X-ray absorption spectroscopy to characterize dissolved and particulate phosphorus species, respectively. In soil and sediment samples reacted with ribonucleotides, we uncover the abiotic production of particulate inorganic phosphate associated specifically with iron oxides. Reactions of various organic phosphorus compounds with the different minerals identified in the environmental samples reveal up to twenty-fold greater catalytic reactivities with iron oxides than with silicate and aluminosilicate minerals. Importantly, accounting for inorganic phosphate both in solution and mineral-bound, the dephosphorylation rates of iron oxides were within reported enzymatic rates in soils. Our findings thus imply a missing abiotic axiom for organic phosphorus mineralization in phosphorus cycling.

Prebiotic chemical reactivity in solution with quantum accuracy and microsecond sampling using neural network potentials

While RNA appears as a good candidate for the first autocatalytic systems preceding the emergence of modern life, the synthesis of RNA oligonucleotides without enzymes remains challenging. Because the uncatalyzed reaction is extremely slow, experimental studies bring limited and indirect information on the reaction mechanism, the nature of which remains debated. Here, we develop neural network potentials (NNPs) to study the phosphoester bond formation in water. While NNPs are becoming routinely applied to nonreactive systems or simple reactions, we demonstrate how they can systematically be trained to explore the reaction phase space for complex reactions involving several proton transfers and exchanges of heavy atoms. We then propagate at moderate computational cost hundreds of nanoseconds of a variety of enhanced sampling simulations with quantum accuracy in explicit solvent conditions. The thermodynamically preferred reaction pathway is a concerted, dissociative mechanism, with the transient formation of a metaphosphate transition state and direct participation of water solvent molecules that facilitate the exchange of protons through the nonbridging phosphate oxygens. Associative-dissociative pathways, characterized by a much tighter pentacoordinated phosphate, are higher in free energy. Our simulations also suggest that diprotonated phosphate, whose reactivity is never directly assessed in the experiments, is significantly less reactive than the monoprotonated species, suggesting that it is probably never the reactive species in normal pH conditions. These observations rationalize unexplained experimental results and the temperature dependence of the reaction rate, and they pave the way for the design of more efficient abiotic catalysts and activating groups.

Solar water splitting Pt-nanoparticle photosystem I thylakoid systems: Catalyst identification, location and oligomeric structure

Photosynthetic conversion of light energy into chemical energy occurs in sheet-like membrane-bound compartments called thylakoids and is mediated by large integral membrane protein-pigment complexes called reaction centers (RCs). Oxygenic photosynthesis of higher plants, cyanobacteria and algae requires the symbiotic linking of two RCs, photosystem II (PSII) and photosystem I (PSI), to split water and assimilate carbon dioxide. Worldwide there is a large research investment in developing RC-based hybrids that utilize the highly evolved solar energy conversion capabilities of RCs to power catalytic reactions for solar fuel generation. Of particular interest is the solar-powered production of H2, a clean and renewable energy source that can replace carbon-based fossil fuels and help provide for ever-increasing global energy demands. Recently, we developed thylakoid membrane hybrids with abiotic catalysts and demonstrated that photosynthetic Z-scheme electron flow from the light-driven water oxidation at PSII can drive H2 production from PSI. One of these hybrid systems was created by self-assembling Pt-nanoparticles (PtNPs) with the stromal subunits of PSI that extend beyond the membrane plane in both spinach and cyanobacterial thylakoids. Using PtNPs as site-specific probe molecules, we report the electron microscopic (EM) imaging of oligomeric structure, location and organization of PSI in thylakoid membranes and provide the first direct visualization of photosynthetic Z-scheme solar water-splitting biohybrids for clean H2 production.

Application of gas diffusion electrodes in bioeconomy: An update.

The transition of today's fossil fuel based chemical industry toward sustainable production requires improvement of established production processes as well as development of new sustainable and bio-based synthesis routes within a circular economy. Thereby, the combination of electrochemical and biotechnological advantages in such routes represents one important keystone. For the electrochemical generation of reactants from gaseous substrates such as O2 or CO2 , gas diffusion electrodes (GDE) represent the electrodes of choice since they overcome solubility-based mass transport limitations. Within this article, we illustrate the architecture, function principle and fabrication of GDE. We highlight the application of GDE for conversion of CO2 using abiotic catalysts for subsequent biosynthesis as well as the application of microbial catalysts at GDE for CO2 conversion. The reduction of oxygen at GDE is summarized for the application of oxygen depolarized cathodes in microbial fuel cells and generation of H2 O2 to drive enzymatic reactions. Finally, engineering aspects such as scale-up and the modeling of GDE-based processes are described. This review presents an update on the application of GDE in bio-based production systems and emphasizes their large potential for sustainable development of new pathways in bioeconomy.

Flow Channel Architecture and Diffusion Characteristics of Nonenzymatic Electrochemical Glucose Fuel Cells with Proton Exchange Membrane

A nonenzymatic glucose fuel cell directly oxidizes glucose to gluconic acid as a Pt-based abiotic catalyst in a proton exchange membrane environment and has various advantages (e.g., biocompatibility, chemical stability, high ionic conductivity). We report the permeability of a less hydrophobic diffusion layer for three flow-field designs (serpentine, interdigitated, and parallel). In all cases, as the channel width of the flow path increases, the power density increases and the Ohmic resistance decreases. The serpentine shape (channel and rib widths: 1.5 and 0.5 mm, respectively) exhibits remarkable maximum power and current densities (cell voltage: 60 mV) of 103.4 μW cm -2 and 1,273 μA cm -2 compared to those of the parallel (46.5 μW cm -2 , 683 μA cm -2 ) and interdigitated (74.0 μW cm -2 , 878 μA cm -2 ) shapes, respectively. Furthermore, permeability and performance analyses according to the single-cell temperature, glucose concentration, and flow rate changes provide various perspectives on glucose fuel cells.

(Digital Presentation) Microbial Fuel Cells: Electrochemical Property and Long-Term Stability Improvement

The microbial fuel cells (MFCs) are bioelectrochemical devices to convert chemical energy into electricity using a microorganism, without relying on abiotic catalysts and fossil fuels. The microbes enable proton production and electron transfer by oxidizing organic matters, which can be from wastewater, biomass, and other feedstocks. The electrons flow will produce a direct electrical current, causing the potential differences between the anode and cathode compartments.The aromatic sulfonation of membrane may result in acidity changes in the anode, causing microbe inhibitions. The PVA based novel membrane was developed and used as the electrolyte to overcome the above problems. The brewer’s yeast (S. cerevisiae) as a biocatalyst was used in MFCs due to the resilience to environmental changes and simple mechanism of electron transfer. The S. cerevisiae an eukaryote was found to easily retrofit into ethanol plants for in situ power generation, which were found improve the microbial fuel cell performance by our study.This study indicated that anodic biofilm modification using nanoparticles is an effective approach to improve electrochemical activities due to their high surface area and high electronic conductivity. The red-light facilitates the efficient electron transfer through mediated redox couples within the anodic biota-anchored films. These redox mediators may represent an electronic network permeating the biofilm that can promote long-range electrical transfer in an energy-efficient manner, as a result of increasing MFC electricity production. As society migrates from consumption of gasoline to low carbon-based fuels, the MFCs becomes important to produce electrical energy with near zero net emission. Figure 1

Cobalt valence modulating in CoO incorporated carbon nanofiber for enhanced glucose electrooxidation

Glucose fuel cells (GFCs) driven by abiotic catalysts are promising green power sources for portable or wearable devices. In this work, a CoO x incorporated carbon nanofiber (CoO x @CNF) catalyst with mixed valences cobalt oxides have been developed through partial oxidation of pyrolyzed electrospun Co 2+ /poly acrylonitrile fibers. The cobalt valence modulating could be achieved via regulating the incorporation ratio of cobalt acetate in precursors or the oxidation temperature of the pyrolyzed fibers. Electrocatalytic analyses show that the presence of CoO in CoO x @CNF will provide more active sites for glucose electrooxidation, and thus enhance the electrocatalytic performance significantly. As a result, the glucose fuel cell built with the CoO x @CNF anode containing both CoO and Co 3 O 4 delivered a maximum power density of 270 μW cm −2 , which is higher than that of other reported Co 3 O 4 based GFCs. This work provides a simple strategy to develop excellent transition metal catalysts for GFCs to expand their applications in portable and wearable energy devices. • CoO x incorporated carbon nanofibers were developed through partial oxidation of pyrolyzed electrospun Co 2+ /poly acrylonitrile fibers. • Cobalt valence modulating was achieved via regulating the oxidation temperature of the pyrolyzed fibers. • Presence of CoO increased the ratio of Co 2+ in CoO x @CNF that provide more active sites for glucose electrooxidation. • CoO x @CNF anode that containing both CoO and Co 3 O 4 delivers superior performance to other reported Co 3 O 4 based GFCs. • CoO x @CNF also achieves excellent performance in wearable patch type GFCs.

Rethinking the biotic and abiotic remineralization of complex phosphate molecules in soils and sediments

Phosphorus (P) is an essential macronutrient for all living organisms. Despite a diversity of P compounds in the environment, orthophosphate is the most bioavailable form of P. Remineralization of complex P molecules (e.g., organic P and phosphoanhydrides) into orthophosphate is traditionally considered to be carried out primarily by enzymes. Natural minerals are recently viewed to be abiotic catalysts (as compared to the organic phosphatases) to facilitate the cleavage of terminal P–O–C/P bonds and remineralization of complex P compounds. However, quantitative comparison between biotic and abiotic remineralization pathways of complex P molecules is still missing, impeding our capability to assess the importance and contribution of abiotic P remineralization in the environment. This study compares the hydrolysis rates of six organic phosphates and three inorganic phosphoanhydrides by representative enzymes (acid and alkaline phosphatases) and natural oxide minerals (hematite, birnessite, and boehmite). The results show that enzymes and minerals have different substrate preferences. Specifically, alkaline phosphatase hydrolyzes phosphate monoesters faster than phosphoanhydrides, whereas acid phosphatase and minerals show higher hydrolysis rates toward phosphoanhydrides than phosphate monoesters. Although the hydrolysis rates by enzymes (~μM hr−1) are orders of magnitude higher than those by minerals (~μM d−1), normalization of the rates by the natural abundance of enzymes and minerals leads to comparable contributions of both processes in soils and sediments. These results highlight the significance of natural minerals in the remineralization of complex P compounds, a process that was traditionally overlooked but with important implications for constraining P biogeochemical cycling in the environment.

Pt Concave Nanocubes with High-Index Facets as Electrocatalysts for Glucose Oxidation

The modification of the surface atomic arrangements, especially the exposure of high-index facets, has been considered as a valid strategy to strengthen the catalytic performance of Pt-based nanocrystals. In this article, Pt concave nanocubes (Pt CNCs) with exposed high-index (510) facets are facilely synthesized through a hydrothermal method. Polyvinylpyrrolidone (PVP) and glycine are required for shape control. The mechanism of electrocatalytic oxidation toward glucose by Pt CNCs is fully discussed. The exposed high-index facets consist of abundant low-coordinated atoms (containing edges, steps, and kinks), can supply sufficient active sites for the adsorption of reactants and intermediate species, and thus enhance the catalytic activity in glucose oxidation. By using saturated calomel electrode as the reference electrode, a 1 cm2 platinum sheet as the counter electrode, and glassy carbon electrode (GCE) as the working electrode, the Pt CNC catalyst-decorated GCE exhibits higher peak current densities of 0.25, 0.15, and 0.56 mA cm–2 than those of the commercial Pt/C (10 wt. %)-modified GCE. The Pt CNC catalyst shows a rapid response toward the changes in glucose concentration. The electrocatalytic oxidation of glucose exhibits better performance in neutral and alkaline conditions than in an acidic electrolyte. Above all, the prepared Pt CNC catalysts with high-index (510) facets are expected for their wide use as abiotic catalysts in the electrocatalytic oxidation of glucose.

Tools and Methods for Investigating Synthetic Metal-Catalyzed Reactions in Living Cells.

Although abiotic catalysts are capable of promoting numerous new-to-nature reactions, only a small subset has so far been successfully integrated into living systems. Research in intracellular catalysis requires an interdisciplinary approach that takes advantage of both chemical and biological tools as well as state-of-the-art instrumentations. In this perspective, we will focus on the techniques that have made studying metal-catalyzed reactions in cells possible using representative examples from the literature. Although the lack of quantitative data in vitro and in vivo has somewhat limited progress in the catalyst development process, recent advances in characterization methods should help overcome some of these deficiencies. Given its tremendous potential, we believe that intracellular catalysis will play a more prominent role in the development of future biotechnologies and therapeutics.

Glucose-Oxygen Biofuel Cell with Biotic and Abiotic Catalysts: Experimental Research and Mathematical Modeling

The demand for alternative sources of clean, sustainable, and renewable energy has been a focus of research around the world for the past few decades. Microbial/enzymatic biofuel cells are one of the popular technologies for generating electricity from organic substrates. Currently, one of the promising fuel options is based on glucose due to its multiple advantages: high energy intensity, environmental friendliness, low cost, etc. The effectiveness of biofuel cells is largely determined by the activity of biocatalytic systems applied to accelerate electrode reactions. For this work with aerobic granular sludge as a basis, a nitrogen-fixing community of microorganisms has been selected. The microorganisms were immobilized on a carbon material (graphite foam, carbon nanotubes). The bioanode was developed from a selected biological material. A membraneless biofuel cell glucose/oxygen, with abiotic metal catalysts and biocatalysts based on a microorganism community and enzymes, has been developed. Using methods of laboratory electrochemical studies and mathematical modeling, the physicochemical phenomena and processes occurring in the cell has been studied. The mathematical model includes equations for the kinetics of electrochemical reactions and the growth of microbiological population, the material balance of the components, and charge balance. The results of calculations of the distribution of component concentrations over the thickness of the active layer and over time are presented. The data obtained from the model calculations correspond to the experimental ones. Optimization for fuel concentration has been carried out.

Design and Engineering of Metal Catalysts for Bio-orthogonal Catalysis in Living Systems.

In the past two decades, bio-orthogonal transformations mediated by biocompatible metal catalysts in living systems have shown enormous potential in both synthetic biology and medicinal chemistry. These metal-mediated bio-orthogonal reactions, many of which could not be accomplished by natural enzymes, have created more possibilities in organic chemistry and biological sciences. Despite all of the challenges for making those abiotic catalysts work in complicated biological environments, many catalytic systems working in living systems have been reported, mediating different transformations such as uncaging of fluorescent probes, pro-drug activation, glycan or protein activation, labeling of proteins or cell surfaces, and in situ drug synthesis. This review categorizes and summarizes the recent development of synthetic metal catalysts for bio-orthogonal reactions in living systems within two decades. Ranging from simple metal complexes and macromolecular-scaffold-based catalytic systems to heterogeneous nanomaterial-based systems, we show those catalysts of diverse nature and highlight the strategies for their design and engineering. We analyze and describe the structure-property relationship of those biocompatible metal catalysts and show the importance of structural diversification and optimization for their potential applications. A brief overview of metal-mediated bio-orthogonal reactions for biological applications is also given, and the challenges and opportunities of this field are discussed from a long-term perspective.

Synthesis and evaluation of Pt/rGO as the anode electrode in abiotic glucose fuel cell: Near to the human body physiological condition

In this research, abiotic catalyst 40 wt% Pt/rGO is successfully synthesized via chemical reduction method with an average particle size of 3 nm (characterized by TEM and XRD), and activity of it as anode catalyst for glucose oxidation is evaluated in phosphate-buffered saline (PBS, pH = 7.4) in the presence of 5 mM glucose (near-human body physiological concentrations).The fuel cell testing is carried out in a two-chamber abiotic glucose fuel cell (AGFC) utilizing Pt/rGO as the anode catalyst and PBS/glucose as the feed. Furthermore, effect of circulated fuel (based on human arm's vein blood flow rate, 0.33 mLs−1) is also investigated for implantable purposes and is compared to stationary fuel; 10% increase in the AGFC voltage in contrast to 23% cell voltage drop respectively under 0.01 mAcm−2 current density over 15 h. Results indicate that Pt/rGO is a promising catalyst for AGFCs to power implantable devices.

Cancer-derived exosomes loaded with ultrathin palladium nanosheets for targeted bioorthogonal catalysis.

The transformational impact of bioorthogonal chemistries has inspired new strategies for the in vivo synthesis of bioactive agents through non-natural means. Among these, palladium (Pd) catalysts have played a prominent role in the growing subfield of bioorthogonal catalysis by producing xenobiotics and uncaging biomolecules in living systems. However, delivering catalysts selectively to specific cell types still lags behind catalyst development. Here we have developed a bio-artificial device consisting of cancer-derived exosomes loaded with Pd catalysts by a method that enables the controlled assembly of Pd nanosheets directly inside the vesicles. This hybrid system mediates Pd-triggered dealkylation reactions in vitro and inside cells and displays preferential tropism for their progenitor cells. The use of Trojan exosomes to deliver abiotic catalysts into designated cancer cells creates the opportunity for a new targeted therapy modality: exosome-directed catalyst prodrug therapy, whose first steps are presented herein with the cell-specific release of the anticancer drug panobinostat.

Raney-platinum thin film electrodes for the catalysis of glucose in abiotically catalyzed micro-glucose fuel cells

Fuel cells capable of synthetic glucose catalysis have revolved around the implementation of abiotic catalysts that require extreme acid and alkaline environments. These are not compatible with implantable medical sensor systems, and hence, there is a need to develop abiotic catalysts that operate at neutral pH. This paper presents structural and electrochemical characteristics of a nanoporous electrode designed for abiotic glucose oxidation in the presence of oxygen in neutral physiological media. The electrode was fabricated by annealing e-beam deposited thin films of platinum (Pt) and nickel (Ni) into a Pt–Ni alloy on a silicon substrate. The porous nature of the alloy enhances electrochemical properties by increasing the real surface area ~ 500 times compared to the geometric surface area of as-prepared multilayer thin films. This was reflected in the exchange current density of the electrode annealed at 800 °C being twice that of the electrode annealed at 650 °C. The cell voltage increase, due to the addition of dissolved physiological oxygen of 2 ppm, was about 100 ± 8 mV under a load current density of 2 µA cm−2. After running for 72 h in a physiological saline solution with 5 mM glucose, the increase in the electrode potential was only 23 µV h−1. These results suggest that the nanoporous Pt–Ni alloy anode offers an improved catalytic stability with time and should be a viable candidate for use in abiotic catalyzed glucose fuel cell systems operating under physiological conditions.

Bioelectrochemical Nitrogen Fixation (e-BNF) Towards the Electrosynthesis of Biomass

The industrial synthesis (Haber-Bosch process) of mineral-N has been showing its dark side. Facing the enormous challenge of feeding humankind new technological solutions should enable sustainable nitrogen (N) fixation, to preserve soil fertility. We introduce a new type of microbial electrosynthesis, aimed at simultaneously fixing N2 and inorganic carbon. In this new perspective, the aim is enhancing biological nitrogen fixation by electrostimulation of complex microbial communities, to produce whole biomass, which can be used as soil fertilizer. Two preliminary contributions in this field reported: a) a bioelectrochemical version of the Haber-bosh process, where methyl viologen shuttled electrons to purified nitrogenase enzymes (Milton et al., 2017) and b) the stimulation of N-fixation in a pure planktonic culture of X. autotrophicus by H2-evolution with a specific abiotic catalyst (Liu et al., 2017). Here, a cathodic biofilm was enriched in electro-active autotrophic nitrogen fixers, starting from a mixed microbial culture. The cathode, a carbon-fibers conductor, was kept under constant polarization (-0.7 V vs SHE). Biomass (in the biofilm, as well as in the bulk liquid phase) was synthesized at significantly higher rates (up to 18-fold), as compared to controls kept at open circuit (OC). Along over 100 days, electron transfer had increased by 30-fold, as compared to abiotic conditions. Metagenomics evidenced Nif genes associated to autotrophs (both Archaea and Bacteria) only in polarized biofilms, while not in OC control. Genes copies encoding for a series of known proteins associated to extracellular electron transfer were double in polarized trials, as compared to controls. The first results of such an approach were recently published in Bioelectrochemistry (Rago et al., 2019). From this proof-of-the-concept, we propose to call this promising field ‘bio-electrochemical nitrogen fixation (e-BNF)’, that deserve future research efforts in both fundamentals and applicative aspects. Liu, C., Sakimoto, K.K., Colón, B.C., Silver, P.A., Nocera, D.G., 2017. Ambient nitrogen reduction cycle using a hybrid inorganic–biological system. Proc. Natl. Acad. Sci. 114, 6450–6455. doi:10.1073/pnas.1706371114 Milton, R.D., Cai, R., Abdellaoui, S., Leech, D., De Lacey, A.L., Pita, M., Minteer, S.D., 2017. Bioelectrochemical Haber–Bosch Process: An Ammonia-Producing H2/N2Fuel Cell. Angew. Chemie - Int. Ed. 56, 2680–2683. doi:10.1002/anie.201612500 Rago, L., Zecchin, S., Villa, F., Goglio, A., Corsini, A., Cavalca, L. & Schievano, A. 2019, ‘Bioelectrochemical Nitrogen fixation (e-BNF): Electro-stimulation of enriched biofilm communities drives autotrophic nitrogen and carbon fixation’, Bioelectrochemistry, vol. 125, pp. 105–15. Figure 1

Hydrogen‐Mediated Electron Transfer in Hybrid Microbial–Inorganic Systems and Application in Energy and the Environment

The conversion of electrical energy to chemical energy is a promising approach to store and utilize renewable electricity. Hybrid microbial–inorganic systems incorporating abiotic catalysts with biocatalysts have been proved to efficiently achieve this conversion. To couple electrocatalytic reactions with microorganism metabolism, H2 can be an ideal mediator for energy and electron transfer between electrodes and microorganisms. In hydrogen‐mediated hybrid microbial–inorganic systems, H2 is produced at the cathodes with abiotic hydrogen evolution reaction catalysts. H2 then functions as an energy carrier and electron donor for hydrogen‐oxidizing microorganisms. Hybrid microbial–inorganic systems have been prevalently used for energy and environmental applications. Herein, the principle, applications, and current challenges of the hybrid microbial–inorganic systems are summarized.

A redox fuel cell capable of converting biofuels to electricity at high rate

Membraneless nanofluidic fuel cells are devices that utilize fluid flow through nanoporous media which serve as three-dimensional electrodes. In the case of hybrid fuel cells (HFC) an enzymatic and an abiotic catalyst are incorporated on the electrodes. Here we compared two different HFC. In the first one (HFC-1), glucose oxidase- and Pt-based electrodes were used as bioanode and cathode respectively. This cell reached an open circuit voltage (OCV) of 0.55 V and a maximum power density of 5.7 mWcm−2. In the second one (HFC-2), AuAg- and laccase-based electrodes were used as anode and biocathode respectively. This cell exhibited an OCV of 0.91 V and a maximum power density of 17 mWcm−2. Finally, enzymatic electrodes were used to develop a high performance biofuel cell (3.2 mWcm−2) that exhibited high stability over 4 days. These preliminary results indicate that the incorporation of enzymes into the 3D carbon structures is an efficient alternative for miniaturized nanofluidic power sources.

Cellular and non-cellular mineralization of organic carbon in soils with contrasted physicochemical properties

It has been recently demonstrated that soil organic carbon (SOC) mineralization is supported by intracellular respiration of heterotrophic microorganisms and by non-cellular oxidative processes. However, little is known about the prevalence and drivers of non-cellular SOC mineralization among soils. In this study, untreated and gamma-irradiated soils sampled along a latitudinal gradient and exhibiting contrasted physicochemical properties were incubated in order to quantify potential non-cellular SOC mineralization and to identify its sensibility to soil properties. In sterilized and unsterilized soils, CO2 emission mirrored O2 consumption signifying the presence of several coupled redox reactions transferring electrons from organic C to intermediate acceptors and to O2. This supports the idea that non-cellular mineralization results from extracellular oxidative metabolisms catalyzed by soil enzymes and/or abiotic catalysts. Our findings also show that non-cellular SOC mineralization is ubiquitous and contributes to 24% of soil respiration on average. Cellular and non-cellular SOC mineralization are positively linked but the contribution of non-cellular processes to soil CO2 emissions increases with dissolved organic carbon concentration.