Type Of Electrochemical Reactor Research Articles

A critical assessment of the effect of carbon-based cathode properties on the in situ electrogeneration of H2O2

In the last few years, the in situ H2O2 electrogeneration through the 2e− oxygen reduction reaction (ORR) pathway has increasingly intrigued the scientific community. In particular, a wide experimental campaign has addressed the synthesis of different carbonaceous cathodes. This has resulted in a high number of 2D and 3D cathode materials, either pristine or modified, whose ability to electrogenerate H2O2 in an efficient manner has been tested in different types of electrochemical reactors. Although there is some experimental work correlating the properties of cathode materials with the H2O2 production efficiency, there is no systematic study on this subject. The purpose of this critical review, which is focused on the literature published within the period 2010-2022, is to elucidate the role of the interfacial properties of carbonaceous cathodes in this field. These cathodes can be classified in two categories according to their structure (i.e., crystalline and fibrous), and in five sub-categories: reticulated vitreous carbon (RVC), graphite, carbon felt, graphite felt and gas-diffusion electrode (GDE). These categories are briefly introduced and the performance of materials is compared. Additionally their interfacial properties (hydrophilicity/hydrophobicity, O 1s/C 1s ratio, pore size and specific surface area) are analyzed, trying to show their influence on the cathode performance in terms of current efficiency. The durability of the cathodes is also examined, along with density functional theory (DFT) studies conducted for the 2e− ORR. Finally, general conclusions and recommendations for future research are presented.

Revealing the Critical Challenges in State-of-the-Art Electrochemical Nitrogen Fixation Research

The energy-intensive Haber-Bosch process fixes around 140 million metric tons of molecular nitrogen (N2) annually worldwide into ammonia (NH3) despite its harsh conditions1. The electrochemical nitrogen reduction reaction (NRR) has been regarded as a promising alternative to the Haber-Bosch process, allowing for distributed and onsite NH3 production, and potentially can accelerate the decoupling of the ammonia industry with the use of fossil fuels2. The prosperity of NRR research under environmentally benign conditions in the past few years, however, has been challenged by the recent questioning on the source of produced NH3 in many systems3,4, due to the wide existence of active nitrogen species and the absence of direct evidence on the conversion of N2 (that is, quantitative analysis of 15NH3 production in the electrolytic experiments with 15N2).In search of effective strategies as solutions to these critical challenges, here we propose a reliable protocol for impurities screening in NRR systems. In particular, suggested procedures to examine and eliminate the N-containing species in the electrolyte salts, catalyst materials, and feeding gases will be presented based on our experimental results. We also recommend a gas circulation system for cost-effective 15N2 experiments with improved accuracy in the determination of 15NH3 production as the true N2 fixation performance. Gas permeation and co-generation of hydrogen (H2) are taken into account to ensure that 15N2 can be well confined in the system for stable long-term operation. Such a system is adaptable to different types of electrochemical reactors, making it possible for measuring and reporting 15NH3 production as a routine activity in future NRR research.

Characterization of hydrodynamics and electrochemical treatment of dye wastewater in two types of tubular electrochemical reactors

Electrochemical treatment is an environmentally friendly method of removing pollutants from industrial wastewater, and tubular electrochemical reactor is one kind of electrochemical reactor. However, the flow field on the electrode surface in a traditional concentric tubular reactor is not homogeneous, leading to low treatment efficiency of the reactors. Therefore, a new tubular electrochemical reactor based on spiral flow caused by a turbulence promoter is presented. In this work, fluid flow and hydrodynamics of the new tubular electrochemical reactor using computational fluid dynamics (CFD) method are studied by comparing them to the traditional one. The electro-oxidation of methylene blue simulation wastewater treatment was developed to analyze the processing efficiency of the two types of electrochemical reactors. In the new tubular electrochemical reactor, due to the presence of spiral turbulence promoter, the mean flow rate and turbulent intensity were clearly increased by 500-700% and nearly 200% compared to that of the traditional one, respectively. Under the same inlet-velocity, the removal rates of wastewater in the new tubular electrochemical reactor were also improved.

Characterization of hydrodynamics and mass transfer in two types of tubular electrochemical reactors

Electrochemical treatment is an environmentally friendly method of removing pollutants from industrial wastewater. The tubular electrochemical reactor is one kind of electrochemical reactor. The current density distribution on the electrode surface in a traditional concentric tubular reactor is not homogeneous and the working area of the anodes and cathodes is unequal. Therefore, a novel tubular electrochemical reactor based on plug flow fluid orthogonal with mesh plate electrodes is presented. In this work, fluid flow and hydrodynamics of the vertical-flow tubular electrochemical reactor, such as velocity distribution and turbulent intensity distribution using computational fluid dynamics (CFD) method, are studied by comparing them to the traditional one. The electro-oxidation of phenol simulation wastewater treatment was developed to analyze the mass transfer performance of the two types of electrochemical reactors. In the novel tubular electrochemical reactor, due to the presence of mesh electrodes, the velocity distribution tended to be more homogeneous. In fact, the turbulent intensity clearly increased by 200% around the electrode surface. The kinetics of organic compounds removal in the novel tubular electrochemical reactor was also improved. Under the same flow rate, the improvement of the mass transfer coefficient for the novel tubular electrochemical reactor was more than twice that of the traditional tubular electrochemical reactor.

Combined technology for clomazone herbicide wastewater treatment: three-dimensional packed-bed electrochemical oxidation and biological contact degradation

The clomazone herbicide wastewater was treated using a combined technology composed of electrochemical catalytic oxidation and biological contact degradation. A new type of electrochemical reactor was fabricated and a Ti/SnO2 electrode was chosen as the anode in electrochemical-oxidation reactor and stainless steel as the cathode. Ceramic rings loaded with SnO2 were used as three-dimensional electrodes forming a packed bed. The operation parameters that might influence the degradation of organic contaminants in the clomazone wastewater were optimized. When the cell voltage was set at 30 V and the volume of particle electrodes was designed as two-thirds of the volume of the total reactor bed, the chemical oxygen demand (COD) removal rate could reach 82% after 120 min electrolysis, and the ratio of biochemical oxygen demand (BOD)/COD of wastewater increased from 0.12 to 0.38. After 12 h degradation with biological contact oxidation, the total COD removal rate of the combined technology reached 95%, and effluent COD was below 120 mg/L. The results demonstrated that this electrocatalytic oxidation method can be used as a pretreatment for refractory organic wastewater before biological treatment.

Electrolytic Reactors for the Recovery of Cadmium from Leaching Solutions

A study has been made of the cathodic deposition of cadmium ions from artificial aqueous and dilute solutions produced by the leaching of spent nickel-cadmium batteries. These solutions contained about 20 g/L Cd, 50 g/L Ni and 1 g/L Co. Two types of electrochemical reactors have been used: a parallel-plate reactor and a packed bed reactor with and without solution recirculation. The deposition processes were carried out galvanostatically and the effect of several electrolysis parameters on the recovery of cadmium was analysed. The concentrations of CdSO4 during and after electrodeposition were determined by atomic absorption spectroscopy. The minimum electrode potentials required for electrodeposition to be achieved were established; in addition the composition of the electrodeposits was also estimated. Extraction efficiencies of 80% Cd were achieved. Electrodeposit compositions were about 70% Cd, 10 % Ni, < 0.5% Co, and ∼20% Na2SO4, Fe, oxides. It has been shown that the parallel-plate reactor is the most suitable for our purpose leading to figures of merit with high efficiency values.

Electrochemical water disinfection Part III: Hypochlorite production from potable water with ultrasound assisted cathode cleaning

A new type of electrochemical reactor for use in electrochemical water disinfection was tested. To solve the problem of the formation of calcium carbonate scales on the cathode surface a cathode which simultaneously acts as a sonotrode was used. This sonotrode is an efficient means for in situ cleaning the cathode surface from calcareous deposits formed during hydrogen evolution from potable water. The production rate of active chlorine from potable water in the new reactor in dependence on current, ultrasound intensity, and flow-through velocity was measured. The production of active chlorine is not significantly changed by the effect of ultrasound.

Reduction of metal ions in dilute solutions using a GBC reactor. Part I: Experimental study on the laboratory scale reduction of ferric ions

To reduce metal ions in dilute solutions a new type of electrochemical reactor has been developed: the GBC-reactor. This reactor consists of a gas diffusion electrode coupled with a packed bed electrode. The working principle of the reactor is based upon two main reactions: the catalytic oxidation of hydrogen gas in the gas diffusion electrode and the simultaneous reduction of metal ions on the packed bed electrode. This process occurs spontaneously without the need for an external power supply when the Gibbs free energy of the total reaction is negative. To study the behaviour of the reactor the reduction of ferric ions was used as a model system. The experimental results, obtained from varying a number of key process parameters, could be described using a very simple macroscopic rate equation. It is concluded that the reduction of ferric ions in a GBC-reactor is controlled by both mass transfer and electrochemical kinetics. To carry out scale-up and optimization studies a reactor model incorporating the potential distribution in the packed bed electrode is, however, necessary.

A comparison of the performance of electrochemical reactor designs in the treatment of dilute solutions

The performance and efficiency of five different types of electrochemical reactors were compared, using the test reaction: Cu 2+Cu − 2e. The cell types used comprised parallel plate with forced flow, the same design packed with Netlon® and glass beads respectively between the parallel plates, a cell using mesh electrodes and lastly a packed bed type reactor. The experimentally obtained limiting current densities are compared with predicted values and cell performances is discussed in terms of these and other parameters such as pressure-drop across the cells.