Steps, hops and turns: examining the effects of channel shapes on mass transfer in continuous electrochemical reactors

Solution moving through an electrode, hence hopping from one electrode to another, has the greatest effect on an electrochemical reaction when compared to simple turns within a flow channel.

Thermodynamic analysis of electrochemical synthesis of ammonia in solid-state proton-conducting electrochemical reactors with considering interfacial potential steps

Ammonia (NH3) as a carbon-free hydrogen carrier shows great potential as fuel and its production at mild conditions is desired. NH3 synthesis at atmospheric pressure can be realized in solid-state...

Response of methanogen communities to the elevation of cathode potentials in bioelectrochemical reactors amended with magnetite

Electromethanogenesis refers to the process where methanogens utilize current for the reduction of CO 2 to CH 4 . Setting low cathode potentials is essential for this process. In this study, we test if magnetite, an iron oxide mineral widespread in the environment, can facilitate the adaption of methanogen communities to the elevation of cathode potentials in electrochemical reactors. Two-chamber electrochemical reactors were constructed with inoculants obtained from paddy field soil. We elevated cathode potentials stepwise from the initial -0.6 V vs the standard hydrogen electrode (SHE) to -0.5 V and then to -0.4 V over the 130 days acclimation. Only weak current consumption and CH 4 production were observed in the bioreactors without magnetite. But significant current consumption and CH 4 production were recorded in the magnetite bioreactors. The robustness of electro-activity of the magnetite bioreactors was not affected by the elevation of cathode potentials from -0.6 V to -0.4 V. But, the current consumption and CH 4 production were halted in the bioreactors without magnetite when the cathode potentials were elevated to -0.4 V. Methanogens related to Methanospirillum were enriched on the cathode surfaces of magnetite bioreactors at -0.4 V, while Methanosarcina relatively dominated in the bioreactors without magnetite. Methanobacterium also increased in the magnetite bioreactors but stayed off electrodes at -0.4 V. Apparently, the magnetite greatly facilitates the development of biocathodes, and it appears that with the aid of magnetite, Methanospirillum spp. can adapt to the high cathode potentials performing efficient electromethanogenesis. IMPORTANCE Converting CO 2 to CH 4 through bioelectrochemistry is a promising approach to the development of green energy biotechnology. This process however requires low cathode potentials, which takes cost. In this study, we test if magnetite, a conductive iron mineral, can facilitate the adaption of methanogens to the elevation of cathode potentials. In the two-chamber reactors constructed by using inoculants obtained from paddy field soil, biocathodes were firmly developed in the presence of magnetite, whereas only weak activities in CH 4 production and current consumption were observed in the bioreactors without magnetite. The elevation of cathode potentials did not affect the robustness of electro-activity of the magnetite bioreactors over the 130 days acclimation. Methanospirillum were identified as the key methanogens associated with the cathode surfaces during the operation at high potentials. The findings reported in this study shed new light on the adaption of methanogen communities to the elevated cathode potentials in the presence of magnetite.

A Potential–dependent Thiele Modulus to Quantify the Effectiveness of Porous Electrocatalysts

<p>Electrochemical reactors often employ high surface area electrocatalysts to accelerate volumetric reaction rates and increase productivity. While electrocatalysts can alleviate kinetic overpotentials, diffusional resistances at the pore-scale often prevent full catalyst utilization. The effect of intraparticle diffusion on the overall reaction rate can be quantified through an effectiveness factor expression governed by the Thiele modulus parameter. This analytical approach is integral to the development of catalytic structures for thermochemical processes and can be extended to electrochemical processes provided the relationship between reaction kinetics and electrode overpotential is incorporated. Here, we derive a potential-dependent Thiele modulus to quantify the effectiveness factor for porous electrocatalytic structures. We apply this mathematical framework to spherical microparticles as a function of applied overpotential across catalyst properties and reactant characteristics. The relative effects of kinetics and mass transport are related to overall reaction rates, revealing markedly lower catalyst utilization at increasing overpotential. Subsequently, we generalize the analysis to alternative catalyst shapes and provide guidance on the design of porous catalytic materials for use in electrochemical reactors.</p>

A Potential–dependent Thiele Modulus to Quantify the Effectiveness of Porous Electrocatalysts

<p>Electrochemical reactors often employ high surface area electrocatalysts to accelerate volumetric reaction rates and increase productivity. While electrocatalysts can alleviate kinetic overpotentials, diffusional resistances at the pore-scale often prevent full catalyst utilization. The effect of intraparticle diffusion on the overall reaction rate can be quantified through an effectiveness factor expression governed by the Thiele modulus parameter. This analytical approach is integral to the development of catalytic structures for thermochemical processes and can be extended to electrochemical processes provided the relationship between reaction kinetics and electrode overpotential is incorporated. Here, we derive a potential-dependent Thiele modulus to quantify the effectiveness factor for porous electrocatalytic structures. We apply this mathematical framework to spherical microparticles as a function of applied overpotential across catalyst properties and reactant characteristics. The relative effects of kinetics and mass transport are related to overall reaction rates, revealing markedly lower catalyst utilization at increasing overpotential. Subsequently, we generalize the analysis to alternative catalyst shapes and provide guidance on the design of porous catalytic materials for use in electrochemical reactors.</p>

Disentangling Syntrophic Electron Transfer Mechanisms in Methanogenesis Through Electrochemical Stimulation, Omics, and Machine Learning

Background: Interspecies hydrogen transfer (IHT) and direct interspecies electron transfer (DIET) are two syntrophy models for methanogenesis. Their relative importance in methanogenic environments is still unclear. Our recent discovery of a novel species Candidatus Geobacter eutrophica with the genetic potential of IHT and DIET may serve as a model species to address this knowledge gap. Results: To experimentally demonstrate its DIET ability, we performed electrochemical enrichment of Ca. G. eutrophica-dominating communities under 0 and 0.4 V vs. Ag/AgCl based on the presumption that DIET and extracellular electron transfer (EET) share similar metabolic pathways. After three batches of enrichment, acetate accumulated in all reactors, while propionate was detected only in the electrochemical reactors. Four dominant fermentative bacteria were identified in the core population, and metatranscriptomics analysis suggested that they were responsible for the degradation of fructose and ethanol to propionate, propanol, acetate, and H2. Geobacter OTU650, which was phylogenetically close to Ca. G. eutrophica, was outcompeted in the control but remained abundant and active under electrochemical stimulation. The results thus confirmed Ca. G. eutrophica’s EET ability. The high-quality draft genome (completeness 99.4%, contamination 0.6%) further showed high phylogenomic similarity with Ca. G. eutrophica, and the genes encoding outer membrane cytochromes and enzymes for hydrogen metabolism were actively expressed. Redundancy analysis and a Bayesian network constructed with the core population predicted the importance of Ca. G. eutrophica-related OTU650 to methane production. The Bayesian network modeling approach was also applied to the genes encoding enzymes for alcohol metabolism, hydrogen metabolism, EET, and methanogenesis. Methane production could not be accurately predicted when the genes for IHT were in silico knocked out, inferring its more important role in methanogenesis.Conclusions: Ca. G. eutrophica is electroactive and simultaneously performs IHT and DIET. The results from the metatranscriptomic analysis have provided valuable information for enrichment and isolation of Ca. G. eutrophica. IHT is predicted to have a stronger impact on methane production than DIET in the electrochemical reactors. The genomics-enabled machine learning modeling approach can provide predictive insights into the importance of IHT and DIET.