Rate controlling reactions for copper corrosion in anaerobic aqueous sulphide solutions

Abstract

The long term corrosion behaviour of copper in anoxic aqueous sulphide solutions has been studied using corrosion potential and electrochemical impedance spectroscopy measurements and scanning electron microscopy on corroded surfaces and cross-sections of surfaces prepared using a focused ion beam. Experiments were conducted in solutions containing either 5×10^?4 or 5×10^?5 mol L^?1 sulphide for 1691 and 4000 h respectively. In the more concentrated solution, a coherent, compact and crystalline chalcocite (Cu₂S) film accumulated on the corroding copper surface. A parabolic growth law was obtained, and the kinetics were controlled by Cu(I) ion transport either through the Cu₂S matrix or along crystalline grain boundaries in the film. In the more dilute solution, the growth of a less crystalline, porous chalcocite layer followed approximately the linear growth kinetics controlled by sulphide ion transport through the pores. If the sulphide was allowed to deplete in the dilute solution, rate control switched to sulphide diffusion in the bulk solution. The implications for waste container corrosion in a nuclear waste repository are discussed.     

Review of the corrosion performance of selected canister materials for disposal of UK HLW and/or spent fuel

Abstract

A review of the corrosion performance of selected canister materials for the disposal of high activity waste in the UK is presented. The canister materials considered are carbon steel, copper, stainless steels, titanium alloys and nickel alloys. The purpose of the review is to provide a high level overview of the technical and scientific issues relating to the use of each of these materials for the disposal of high level waste and spent nuclear fuel in the UK. The advantages and disadvantages of each material are described, as are limiting or ‘critical’ conditions for which the use of a given material is questionable or not recommended.     

Dysprosium doped copper oxide (Cu1-xDyxO) nanoparticles enabled bifunctional electrode for overall water splitting

The production of hydrogen, a favourable alternative to an unsustainable fossil fuel remains as a significant hurdle with the pertaining challenge in the design of proficient, highly productive and sustainable electrocatalyst for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Herein, the dysprosium (Dy) doped copper oxide (Cu_1-xDy_xO) nanoparticles were synthesized via solution combustion technique and utilized as a non-noble metal based bi-functional electrocatalyst for overall water splitting. Due to the improved surface to volume ratio and conductivity, the optimized Cu_1-xDy_xO (x = 0.01, 0.02) electrocatalysts exhibited impressive HER and OER performance respectively in 1 M KOH delivering a current density of 10 mAcm^?2 at a potential of ?0.18 V vs RHE for HER and 1.53 V vs RHE for OER. Moreover, the Dy doped CuO electrocatalyst used as a bi-functional catalyst for overall water splitting achieved a potential of 1.56 V at a current density 10 mAcm^?2 and relatively high current density of 66 mAcm^?2 at a peak potential of 2 V. A long term stability of 24 h was achieved for a cell voltage of 2.2 V at a constant current density of 30 mAcm^?2 with only 10% of the initial current loss. This showcases the accumulative opportunity of dysprosium as a dopant in CuO nanoparticles for fabricating a highly effective and low-cost bi-functional electrocatalyst for overall water splitting.     

Electrochemically active and robust cobalt doped copper phosphosulfide electro-catalysts for hydrogen evolution reaction in electrolytic and photoelectrochemical water splitting

The area of non-noble metals based electro-catalysts with electrochemical activity and stability similar or superior to that of noble metal electro-catalyst for efficient hydrogen production from electrolytic and photoelectrochemical (PEC) water splitting is a subject of intense research. In the current study, exploiting theoretical first principles study involving determination of hydrogen binding energy to the surface of the electro-catalyst, we have identified the (Cu_0.83Co_0.17)₃P: x at. % S system displaying excellent electrochemical activity for hydrogen evolution reaction (HER). Accordingly, we have experimentally synthesized (Cu_0.83Co_0.17)₃P: x at. % S (x = 10, 20, 30) demonstrating excellent electrochemical activity with an onset overpotential for HER similar to Pt/C in acidic, neutral as well as basic media. The highest electrochemical activity is exhibited by (Cu_0.83Co_0.17)₃P:30 at. % S nanoparticles (NPs) displaying overpotential to reach 100 mA cm^?2 in acidic, neutral and basic media similar to Pt/C. The (Cu_0.83Co_0.17)₃P:30 at. % S NPs also display excellent electrochemical stability in acidic media for long term electrolytic and PEC water splitting process [using our previously reported (Sn_0.95Nb_0.05) O₂: N-600 nanotubes (NTs) as the photoanode]. The applied bias photon-to-current efficiency obtained using (Cu_0.83Co_0.17)₃P:30 at. % S NPs as the cathode electro-catalyst for HER in an H-type PEC water splitting cell (～4%) is similar to that obtained using Pt/C (～4.1%) attesting to the promise of this exciting non-noble metal containing system.     

Crevice corrosion of copper for radioactive waste packaging material in simulated groundwater

The investigation described here was conducted to clarify the corrosion behaviour of high level radioactive waste containers made of copper. The influences of oxygen, chloride ion and sulphate ion on copper crevice corrosion were studied in solutions simulating groundwater characteristic of northwest China. The results showed that oxygen, chloride ion and sulphate ion promote crevice corrosion. Chloride ion was found to play a significant role in the crevice corrosion mechanism in copper, but sulphate ion had no effect on the mechanism.     

First-principles investigation of BiVO3 for thermochemical water splitting

Thermochemical water splitting is a promising clean method of hydrogen production of high relevance in a society heavily reliant on fossil fuels. Using evolutionary methods and density functional theory, we predict the structure and electronic properties of BiVO₃. We build on previous literature to develop a framework to evaluate the thermodynamics of thermochemical water splitting cycles for hydrogen production. We use these results to consider the feasibility of BiVO₃ as a catalyst for thermochemical water splitting. We show that for BiVO₃, both the thermal reduction and gas splitting reactions are thermodynamically favorable under typical temperature conditions. We predict that thermochemical water splitting cycles employing BiVO₃ as a catalyst produce hydrogen yields comparable to those of commonly used catalysts.     

Photoelectrolysis of water using thin copper gallium diselenide electrodes

Thin CuGaSe₂ films were deposited by vacuum co-evaporation and characterized for their structure, properties and performance as hydrogen-evolving photoelectrodes. The 0.9 μm thick films were nearly stoichiometric with very slight copper deficiency and showed polycrystalline structure with grain sizes of tens of nanometers. An electrode based on such a film was demonstrated operating with outdoor 1-sun photocurrent of up to 13 mA/cm². Spectral response data show significant incident-photon-to-current efficiency throughout the visible spectrum, peaking at 63% at 640 nm. Photocurrent output under simulated 1-sun Air Mass 1.5 light was stable over 4 h. Unassisted water-splitting is not possible due to high band edge positions, but operation in tandem configuration with a suitable bottom junction is feasible.     

Synthesis of metallic copper nanowires using dielectric barrier discharge plasma and their application in hydrogen evolution reaction

In this study, metallic copper (Cu) nanowires are synthesized by reducing thermally synthesized CuO nanowires under an indigenously developed hydrogen plasma system. The X-ray diffraction (XRD) results of the plasma-synthesized nanowires indicate the presence of metallic copper [(111) and (200)] and the field emission scanning electron microscopy (FESEM) further affirms the findings by presenting a stark difference in contrast of the nanowires before and after plasma treatment with diameters of 50 and 100 nm, respectively. The nanowires are studied for hydrogen evolution reaction in a neutral medium and they show excellent performance than the previously reported studies on bulk copper, with an overpotential of 210 mV at a current density of 10 mA/cm² and an exchange current density of 60 exp-5 A/cm² which is an order of magnitude larger than the reported values on bulk copper. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy indicates that the surface of the nanowires is highly rich in metallic copper resulting in better electrochemical performance of the metallic Cu nanowires in a neutral environment.     

Aromatic amines as proton carriers for catalytic enhancement of hydrogen evolution reaction on copper in acid solutions

The catalytic effect of some aromatic amines towards hydrogen evolution reaction on copper in diluted sulfuric acid solution has been studied. Since amines facilitate the transport of protons from the solution bulk to the interface in the cathodic hydrogen evolution reaction, they are known as proton carriers. The catalytic effect of aniline, N-methylaniline, N-ethylaniline, N,N-dimethylaniline, N,N-diethylaniline, o-toluidine, m-toluidine and p-toluidine has been highlighted by linear sweep voltammetry. The kinetic parameters for the hydrogen evolution reaction (cathodic transfer coefficient 1-α and exchange current density i_o) in the presence of the studied aromatic amines were derived from the Tafel plots. It has been found that the catalytic effect of amines is active even at low concentration. Thus, in 0.5 mol L⁻¹ H₂SO₄ solution the exchange current density increases by two orders of magnitude, from 2.01⋅10⁻⁵ A m⁻² in the absence of aniline to 2.85⋅10⁻³ A m⁻² in the presence of 10⁻⁴ mol L⁻¹ aniline. The influence of amines concentration on the catalytic effect is described in detail for the case of m-toluidine. The results obtained by voltammetry have been compared with electrochemical impedance spectroscopy data. Furthermore, the kinetic parameters for the hydrogen evolution reaction have been determined as a function of temperature and amines concentration.     

Three-dimensional copper cobalt hydroxide electrode for anion exchange membrane water electrolyzer

Anion exchange membrane (AEM) water electrolyzers are promising energy devices for producing low-cost and clean hydrogen using platinum group metals (PGMs). However, AEM water electrolyzers still do not show satisfactory performance due to the sluggish kinetics of the electrodes. In this work, copper cobalt hydroxide (CuCo-hydroxide) nanosheet was synthesized on commercial nickel foam (NF) via electrochemical co-precipitation, and used directly as an oxygen evolution reaction (OER) electrode for an AEM electrolyzer. The interaction between Cu and Co induces a change in the electronic structure of Co(OH)₂ and improves the performance of the OER electrode. In addition, the AEM electrolyzers catalyzed by CuCo(OH)₂ showed high energy conversion efficiency of 73.5%. This work demonstrates that non-PGM based electrodes fabricated using a simple electrochemical co-precipitation apply to AEM electrolyzers for low-cost and clean hydrogen production.     

Hydrogen-enhanced degradation and oxide effects in zirconium alloys for nuclear applications

The zirconium alloys used in nuclear industry include mainly Zr-Sn and Zr-Nb alloys of different chemical composition, microstructure and susceptibility to both hydrogen degradation and oxidation. The hypothetic nuclear accidents can create a real danger to the Zr alloys and stability of parts made of these alloys, and especially such as loss of coolant accident (LOCA) and reactivity initiated accidents (RIA). The hydrogen degradation can manifest itself in an appearance of hydride phases resulting in a substantial loss of plasticity, an increase in ductile-brittle transition, sometimes in a decrease in mechanical strength. The oxidation can prevent the hydrogen entry but at high temperatures the cracking of the oxide layer can form the easy hydrogen diffusion channels. Based on a substantial number of tests made so far and well-known thermodynamic and kinetic parameters, the general microstructure-dependent and temperature-dependent degradation model considering both hydrogen and oxidation could be elaborated.     

Catalytic enhancement of hydrogen evolution reaction on copper in the presence of benzylamine

Benzylamine catalytic effect on the cathodic hydrogen evolution in acid aqueous solution has been studied on copper electrode. Experimental results obtained by voltammetric techniques emphasize that the presence of benzylamine in 1 M sulfuric acid solution enhances the hydrogen evolution reaction (HER). In such a solution, benzylamine is protonated and exists as benzylammonium cation. Kinetic parameters of HER have been determined, observing a significant increase of the exchange current in the presence of benzylamine. Also, a decrease of the cathodic transfer coefficient has been noticed. Activation energy for HER has been computed on the basis of the Arrhenius plots. In the presence of benzylamine the activation energy was 33.0 kJ mol⁻¹, whereas without benzylamine a greater value was obtained: 94.6 kJ mol⁻¹. The catalytic effect of benzylamine was confirmed by electrochemical impedance spectroscopy. The considerable diminution of the double layer capacity is a valid proof of the strong adsorption of benzylamine at the Cu - sulfuric acid solution interface, while the reduction of the charge transfer resistance is a symptom of the enhancement of HER. Ab initio molecular modeling of benzylammonium ion showed that, due to a high value of the dipole moment, the molecules are oriented in the most favorable position for the charge transfer reaction, i.e., with the protonated amino group facing toward the electrode.     

Potential dependent growth of Cu(OH)2 nanostructures on Cu and their thermal conversion to mixed-valent copper oxides p-type photoelectrode

Herein, we report the anodic growth of nanostructured Cu(OH)₂ thin films on the copper surface by potentiostatic and potentiodynamic methods. The phase formation, crystalline feature, morphology and the progressive growth of Cu(OH)₂ thin films were controlled by the applied potential and concentrations of alkali utilized in anodization process. Electrochemical investigations suggest the rapid growth of Cu(OH)₂ and passivation at higher anodization potentials. In contrast, the lower anodization potentials favours the progressive growth of Cu(OH)₂ nanorod like features. The thermal treatment of Cu/Cu(OH)₂ reveals the formation of crystalline mixed copper oxide film with predominantly Cu₂O phase at 673 K and 773 K. Photoelectrochemical investigations of these copper oxide thin films exhibit the p-type behavior with repeatable photovoltage (55 mV) and stable photocurrent responses (20–60 μA cm⁻²). The hydrogen evolution studies show better activity with nanostructured Cu(OH)₂ and copper oxides than with aggregated thin films and bare substrate.     

Lanthanum doped copper oxide nanoparticles enabled proficient bi-functional electrocatalyst for overall water splitting

The need for a clean and an environmentally non-degrading sustainable energy resource has grown worldwide due to the huge depletion of other fuel sources, as a result, production of hydrogen by electrochemical water splitting is considered as a potential answer to this pertaining need. However, development of low-cost electrocatalyst as a replacement for Pt and RuO₂ for both Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER) remains a significant challenge for the production of hydrogen at a larger scale. This study presents the synthesis of non-noble metal-based lanthanum doped copper oxide nanoparticles as a potential bi-functional electrocatalyst for overall water splitting in alkaline electrolyte. The optimized 1% lanthanum (La) doped CuO electrocatalyst exhibits outstanding OER and HER activity in 1.0 M KOH electrolyte posting a potential of 1.552 V vs RHE for OER and −0.173 V vs RHE for HER at a current density of ~10 mAcm⁻². Significantly, the functional bi-catalyst exhibits a low cell voltage of 1.6 V to achieve overall water splitting at a current density of 10 mAcm⁻² along with long-term stability of 13.5 h for a cell voltage of 2.25 V at a constant current density of 30 mAcm⁻² with only 20% initial current lose after 13.5 h. The results demonstrate that the incorporation of the rare-earth element onto CuO nanoparticles has made it a viable high-end non-noble electrocatalyst for overall water splitting.     

Bimetallic metal-organic framework derived electrocatalyst for efficient overall water splitting

The development of bifunctional catalysts that can be applied to both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is widely regarded as a key factor in the production of sustainable hydrogen fuel by electrochemical water splitting. In this work, we present a high-performance electrocatalyst based on nickel-cobalt metal-organic frameworks for overall water splitting. The as-obtained catalyst shows low overpotential to reaches the current density of 10 mA cm⁻² with 249 mV for OER and 143 mV for HER in alkaline media, respectively. More importantly, when the electrolyzer was assembled with the as-prepared catalyst as anode and cathode simultaneously, it demonstrates excellent activity just applies a potential of 1.68 V to achieve 10 mA cm⁻² current density for overall water splitting.     

Effects of temperature on corrosion performances of TiO2/SS316L in supercritical water for hydrogen production

Temperature is the most important factor for hydrogen generation during supercritical water gasification process. However, the increasing temperature could accelerate the corrosion of the reactor material, at the presence of oxygen, as less amount of oxygen can promote the hydrogen production. In this study, we prepared a 0.1 mm thick of TiO₂ coating on the surface of 316L stainless steel (SS316L) to enhance the corrosion resistance of SS316L during hydrogen production process in supercritical water. The influences of temperature (400–500 °C) on surface morphologies and corrosion depth and rate of TiO₂/SS316L were evaluated at 25 MPa with 1000 mg/L oxygen for 80h. Results showed that cracks and pores were present on the surface of TiO₂/SS316L after corroded in SCW for 80h. The crack width and corrosion rate was aggravated at higher temperature. The remained thickness of the coating at 400 °C, 450 °C, 500 °C were 0.08 mm, 0.05 mm and 0.03 mm, respectively. NiO and NiFe₂O₄ were generated around the crack on the surface of TiO₂/316L at 500 °C, the coating had a tendency to peel off the substrate.     

Polyaniline coated copper for hydrogen storage and evolution in alkaline medium

Emeraldine Hydrochloride salt is coated on copper substrate and studied for hydrogen storage and hydrogen evolution reaction in 1 M NaOH. Phenomenological thermodynamic approach demonstrated elsewhere in conjunction with the cyclic voltammetry data is employed to calculate the solvent modified work function for polyaniline coated copper in alkaline medium as ?0.65 eV. The solvated work function is in satisfactory agreement with the band gap difference of π?π* transition in emeraldine base and π- polaron transition in emeraldine salt ca ?0.6 eV as reported in the literature. ¹³C and ¹H NMR studies revealed that polyaniline undergoes switching between emeraldine salt and emeraldine base, before and after hydrogen evolution respectively. The volume of hydrogen evolved on polyaniline coated copper is 1.64 times than that on copper as demonstrated by Gas chromatography. Thus emeraldine salt, when stored in NaOH act as hydrogen storage medium and upon electrochemical perturbation can release hydrogen at controlled rate depending on the scan rate employed.     

CuO/CuBi2O4 bilayered heterojunction as an efficient photocathode for photoelectrochemical hydrogen evolution reaction

The poor photostability and low photoactivity are two bottlenecks limiting the application of CuO and CuBi₂O₄ as competitive candidates for photoelectrochemical (PEC) hydrogen evolution reaction (HER). To overcome the bottlenecks, we constructed a novel CuO/CuBi₂O₄ bilayered structure for PEC HER. The underlying CuO layer functions as the main photoabsorber, while the outside CuBi₂O₄ layer acts as a protection shield. After further decorated with the NiO_x electrocatalysts, the CuO/CuBi₂O₄/NiO_x photocathode exhibits a high photoactivity and remarkable photostability. We ascribe this excellent performance to the following factors: (1) the bilayer structure improves light harvesting efficiency, (2) the outside CuBi₂O₄ enhances the photostability, (3) the favorable band alignment increases charge separation efficiency, and (4) the presence of NiO_x facilitates the charges transfer at the interface. Therefore, this work not only sets a new benchmark efficiency for the CuO and CuBi₂O₄ heterojunction, but also provides principles for designing layered heterojunction for PEC water splitting.     

Effective surface roughening of three-dimensional copper foam via sulfurization treatment as a bifunctional electrocatalyst for water splitting

Cost effective electrocatalysts in water splitting reaction are critically important for the practical application of hydrogen fuel. The surface of three-dimensional copper foam is successfully roughened via one-step sulfurization reaction, and cuprous sulfide is formed on copper foam accordingly, which is denoted as Cu₂S@Cu. The as-prepared Cu₂S@Cu electrocatalyst exhibits remarkable performance on oxygen evolution reaction in basic solution, with a low overpotential of 345 mV to achieve 20 mA cm⁻². Cu₂S@Cu also shows enhanced performance on hydrogen production, compared to the original copper foam. Furthermore, Cu₂S@Cu can work as both cathode and anode in full water splitting, with superior activity to the noble metal-based electrocatalysts under large current densities. This study demonstrates that surface roughening technique on copper foam by sulfurization reaction can be valuable for developing novel copper-based electrocatalysts for water splitting.     

Supercritical water gasification of food waste: Effect of parameters on hydrogen production

Food waste is a type of municipal solid waste with abundant organic matter. Hydrogen contains high energy and can be produced by supercritical water gasification (SCWG) of organic waste. In this study, food waste was gasified at various reaction times (20–60 min) and temperatures (400 °C-450 °C) and with different food additives (NaOH, NaHCO₃, and NaCl) to investigate the effects of these factors on syngas yield and composition. The results showed that the increase in gasification temperature and time improved gasification efficiency. Also, the addition of food additives with Na⁺ promoted the SCWG of food waste. The highest H₂ yield obtained through non-catalytic experiments was 2.0 mol/kg, and the total gas yield was 7.89 mol/kg. NaOH demonstrated the best catalytic performance in SCWG of food waste, and the highest hydrogen production was 12.73 mol/kg. The results propose that supercritical water gasification could be a proficient technology for food waste to generate hydrogen-rich gas products.