Bioinspired Synthesis of Reduced Graphene Oxide-Wrapped Geobacter sulfurreducens as a Hybrid Electrocatalyst for Efficient Oxygen Evolution Reaction

Doping/decorating of graphene or reduced graphene oxide (rGO) with heteroatoms provides a promising route for the development of electrocatalysts which will be useful in many technologies, including water splitting. However, current doping approaches are complicated, not eco-friendly, and not cost-effective. Herein, we report the synthesis of doped/decorated rGO for oxygen evolution reaction (OER) using a simple approach that is cost-effective, sustainable, and easy to scale up. The OER catalyst was derived from the reduction of GO by an exo-electron-transferring bacterium, Geobacter sulfurreducens. Various analytical tools indicate that OER active elements such as Fe, Cu, N, P, and S decorate the rGO flakes. The hybrid catalyst (i.e., Geobacter/rGO) produces a geometric current density of 10 mA cm–2 at an overpotential of 270 mV versus the reversible hydrogen electrode with a Tafel slope of 43 mV dec–1 and possesses high durability, as evidenced through 10 h of stability testing. Electrochemical analyses suggest the importance of Fe and its possible role as an active site for OER. Overall, this work represents a simple approach toward the development of an earth-abundant, eco-friendly, and highly active OER electrocatalyst for various applications such as solar fuel production, rechargeable metal–air batteries, and microbial electrosynthesis

Advancement of a Liquid Scintillation Counter and Semiconductor Alpha Spectroscopy Detector to Estimate the Radon Concentration in Groundwater

Radon is one of the most natural forms of radiation for human exposure. However, high-accuracy measurement of natural radon in water samples is very challenging due to the background correction, data acquisition, and sampling time. Liquid scintillation counter (LSC) and semiconductor alpha spectroscopy detectors are the most commonly used methods of determining radon concentration in water. The present study utilizes both methods to estimate radon in groundwater collected from various locations in the northeast region of Saudi Arabia. The estimated radon concentrations using Hidex 300SL are compared with a Durridge RAD7 detector to evaluate each apparatus’s abilities, advantages, and disadvantages. Both methods show radon concentrations between 0.1 and 3.20 Bq/L with an average of 0.96 Bq/L, with a standard deviation of 0.82 Bq/L. The estimated values are found to be in the safe limit recommended by the USEPA and EAEC and are far below the safe level recommended by UNSCEAR and the WHO. Comparing the estimated radon concentration using the two methods shows that although the two devices have many advantages and disadvantages based on the two different techniques, the experimental results are almost the same with experimental error

Advancement of a Liquid Scintillation Counter and Semiconductor Alpha Spectroscopy Detector to Estimate the Radon Concentration in Groundwater

Radon is one of the most natural forms of radiation for human exposure. However, high-accuracy measurement of natural radon in water samples is very challenging due to the background correction, data acquisition, and sampling time. Liquid scintillation counter (LSC) and semiconductor alpha spectroscopy detectors are the most commonly used methods of determining radon concentration in water. The present study utilizes both methods to estimate radon in groundwater collected from various locations in the northeast region of Saudi Arabia. The estimated radon concentrations using Hidex 300SL are compared with a Durridge RAD7 detector to evaluate each apparatus’s abilities, advantages, and disadvantages. Both methods show radon concentrations between 0.1 and 3.20 Bq/L with an average of 0.96 Bq/L, with a standard deviation of 0.82 Bq/L. The estimated values are found to be in the safe limit recommended by the USEPA and EAEC and are far below the safe level recommended by UNSCEAR and the WHO. Comparing the estimated radon concentration using the two methods shows that although the two devices have many advantages and disadvantages based on the two different techniques, the experimental results are almost the same with experimental error

Investigation of Radon in Groundwater and the Corresponding Human-Health Risk Assessment in Northeastern Saudi Arabia

Radon is one of the most common human exposures as a natural radiation source and can cause lung, colon, and stomach cancer. In this study, groundwater from different wells was collected from the northeastern part of Saudi Arabia. The radon concentration was estimated using an electronic portable radon detector RAD7 with a big-bottle system. The annual effective dose of radon exposure by the ingestion and inhalation of water is calculated using the radon concentration for different age groups to assess the health risk of radon exposure. The calculated annual effective doses are then compared with the international risk limit standard as international organizations direct. The estimated radon concentration for groundwater samples in the searched area was between 0.03 and 3.20 Bq/L, with an average value of 1.16 Bq/L. These estimated values are far below the safety limit set by international organizations. The annual effective dose of radon exposure for infants, children and adults ranged from 0.05 to 16.24 μSv/y, with a mean value of 5.89 μSv/y. The health risk assessed by radon exposure for infants, children and adults was found to be in the safe limit recommended by international organizations

Exploration of reduced graphene oxide microparticles as electrocatalytic materials in vanadium redox flow batteries

Augmenting reaction rates on porous carbon electrodes is critical for reducing the cost of all-vanadium redox flow batteries (VRFBs). To this end, reduced graphene oxide (rGO) based carbons hold promise, demonstrating high specific surface area, chemomechanical stability, and electrochemical activity. While initial efforts have shown that rGOs can enhance VRFB performance, the range of unique processing conditions leads to a collection of materials with disparate elemental composition and porous structure, thus obscuring performance-determining characteristics behind redox reactions and frustrating the development of generalizable design principles. Here, we generate rGO electrocatalysts of nearly identical chemical composition but different textures (i.e., surface area and pore structure) by varying the drying step in the graphene synthesis (i.e., vacuum-drying vs. carbon dioxide critical point drying). We apply spectroscopic and electrochemical techniques on the synthesized rGOs, observing a three-fold increase in BET surface area using critical point drying. We subsequently decorate carbon felt electrodes – both pristine and thermally activated – with rGO microparticles via a flow deposition procedure, and evaluate their performance and durability in a VRFB cell. The synthesis approach and findings described in this work inform and complement efforts to advance the material science and engineering of rGO electrocatalysts

Graphitic Cathodes for Aluminum Batteries with Aqueous Electrolytes

Concerns over lithium-ion battery safety and environmental impact have led to increased exploration of alternative energy storage systems. Of these, aluminum is of particular interest, being environmentally friendly, safe and easy to handle. In this work, we explore graphitic cathodes with an aqueous electrolyte (aluminum trifluoromethanesulfonate) and study their electrochemical performance. Finally, a reduced graphene cathode with tailored porosity results in an eco-friendly and inherently safe rechargeable battery with promising electrochemical performanc

Electrode–Electrolyte Interactions in an Aqueous Aluminum–Carbon Rechargeable Battery System

Being environmentally friendly, safe and easy to handle, aqueous electrolytes are of particular interest for next-generation electrochemical energy storage devices. When coupled with an abundant, recyclable and low-cost electrode material such as aluminum, the promise of a green and economically sustainable battery system has extraordinary appeal. In this work, we study the interaction of an aqueous electrolyte with an aluminum plate anode and various graphitic cathodes. Upon establishing the boundary conditions for optimal electrolyte performance, we find that a mesoporous reduced graphene oxide powder constitutes a better cathode material option than graphite flakes

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

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 has previously been extended to electrochemical processes by accounting for the relationship between reaction kinetics and electrode overpotential. In this paper, we illustrate the method by deriving the expression for the potential-dependent Thiele modulus and using it to quantify the effectiveness factor for porous electrocatalytic structures. Specifically, we demonstrate the application of 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 different catalyst shapes and provide guidance on the design of porous catalytic materials for use in electrochemical reactors

A process to enhance the specific surface area and capacitance of hydrothermally reduced graphene oxide

The impact of post-synthesis processing in reduced graphene oxide materials for supercapacitor electrodes has been analyzed. A comparative study of vacuum, freeze and critical point drying was carried out for hydrothermally reduced graphene oxide demonstrating that the optimization of the specific surface area and preservation of the porous network are critical to maximize its supercapacitance performance. As described below, using a supercritical fluid as the drying medium, unprecedented values of the specific surface area (364 m2 g-1) and supercapacitance (441 F g-1) for this class of materials have been achieved

Methods—A Potential–Dependent Thiele Modulus to Quantify the Effectiveness of Porous Electrocatalysts

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 has previously been extended to electrochemical processes by accounting for the relationship between reaction kinetics and electrode overpotential. In this paper, we illustrate the method by deriving the expression for the potential-dependent Thiele modulus and using it to quantify the effectiveness factor for porous electrocatalytic structures. Specifically, we demonstrate the application of 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 different catalyst shapes and provide guidance on the design of porous catalytic materials for use in electrochemical reactors.</jats:p