Electrochemical science advances最新文献

Marcel Pourbaix (Figure 1) was a Belgian chemist (born in Russia) who greatly contributed to studies on corrosion. His biggest achievement is the derivation of potential-pH diagrams, better known as “Pourbaix Diagrams” (Figure 2a). Pourbaix Diagrams are thermodynamic charts constructed using the Nernst equation. They visualize the relationship between possible redox states of a system, bounded by lines representing the reactions between them under thermodynamic equilibrium. The Pourbaix diagrams can be read much like phase diagrams. In 1963, Pourbaix produced “Atlas of Electrochemical Equilibria in Aqueous Solutions” (Figure 2b), which contains potential-pH diagrams for all elements known at the time. Pourbaix and his collaborators began preparing the work in the early 1950s and continued the diagram updates over many years.

The author declares no conflict of interest.

NaTi₂(PO₄)₃ (NTP) and Na_0.44MnO₂ (NMO), and their derivatives, have emerged as the most promising materials for aqueous Na-ion batteries. For both, NTP and NMO, avoiding the evolution of hydrogen and oxygen is found to be mandatory in order to mitigate material dissolution. Intriguingly, however, no direct determination of the hydrogen and oxygen evolution reactions (HER and OER) has yet been carried out. Using differential electrochemical mass spectrometry (DEMS) we directly identify the onset potentials for the HER and OER. Surprisingly, the potential window is found to be significantly smaller than suggested by commonly employed cyclic voltammetry measurements. CO₂ evolution, upon decomposition of carbon black, is observed at an onset potential of 1.61 V_RHE, which is 0.25 V more cathodic than the OER for the NMO electrode. Our results show that the state-of-the-art carbon additive plays a crucial role in the stability of the positive NMO electrode in the ion battery.

The presently increasing global population demands increased food production. Consequently, phosphate – an indispensable fertilizer component – will be needed in ever greater amounts. Current levels of mining of phosphate's most important constituent element, phosphorus (P), are unsustainable, and P rock is predicted to soon be completely depleted. Because P is a non-renewable resource, techniques to recover and reuse waste phosphate are necessary. Large amounts of unused phosphate exist in both municipal and agricultural wastewater streams, as well as in sewage sludge. Approaches to recovering phosphate from these sources fall into three main categories: biological, chemical, and electrochemical. Biological phosphate recovery has seen some plant-scale use, but significant drawbacks including the complication of operation have prevented it from becoming widespread. The most common method of phosphate recovery, chemical phosphate recovery, has been applied at scale with success due to the stability and reliability of the process. However, disadvantages such as the exorbitant amounts of alkali dosing required to maintain the high pH necessary for phosphate precipitation leave room for improvement. In recent years, electrochemical phosphate recovery has gained traction because of its potential to overcome the weaknesses of traditional chemical approaches by utilizing water electrolysis to induce a high pH without the need for an added base. But before plant-scale electrochemical methods can be considered economically viable, the steep energy requirements of water electrolysis must be mitigated through the development of improved electrocatalysts or circumvented through the discovery and application of new electrochemical processes to generate hydroxyl ions needed to induce a high pH. In this review, the three broad categories of phosphate recovery techniques are discussed and an outlook on the future of electrocatalysis for phosphate recovery is presented. Particularly, the requirements for improved and Earth-abundant electrocatalysts are considered alongside a critical discussion of the possibility of a decentralized network of onsite wastewater treatment facilities powered by renewable electricity.

The electrochemical nitrate reduction reaction (NO₃RR) has the potential for distributed water treatment and renewable chemical synthesis. Cu is an active monometallic electrocatalyst for the NO₃RR in acidic and alkaline electrolytes, where activity is limited by the reduction of adsorbed nitrate to nitrite. Oxygen-vacancy forming metal-oxide supports provide sites for N-O bond activation in thermal reduction, impacting product distribution as well. Here we compare the electrochemical NO₃RR activity of Cu deposited on two metal-oxide supports (cerium dioxide [Cu/CeO_2-δ] and fluorine-doped tin dioxide [Cu/FTO]) to a Cu foil benchmark. Considering activity in phosphate-buffered neutral media, nitrate and adsorbed hydrogen compete for surface sites under NO₃RR conditions. The less-cathodic overpotential on Cu/CeO_2-δ compared to Cu/FTO is attributed to stronger nitrate adsorption, similar to thermal nitrate reduction. Utilization of CeO_2-δ as an electrocatalyst support slightly shifting product distribution toward more oxidized products, either by enhancing nitrate affinity or by a more dynamic process involving the formation and healing of oxygen vacancies (𝑣_O^••). These results suggest supporting catalysts on metal oxides may enhance activity by promoting the adsorption of anionic reactants on cathodic electrocatalysts.

Despite numerous experimental and theoretical studies devoted to the oxygen evolution reaction (OER), the mechanism of the OER on transition metal oxides remains controversial. This is in part owing to the ambiguity of electrochemical parameters of the mechanism such as the Tafel slope and reaction orders. We took the most commonly assumed adsorbate mechanism and calculated the Tafel slopes and reaction orders with respect to pH based on microkinetic analysis using the steady-state approximation. The analysis was performed for an ideal electrocatalyst without scaling of the intermediates as well as for one on the top of a volcano relation and one on each leg of the volcano relation which exhibits scaling of the intermediates. For these four cases, the number of possible Tafel slopes strongly depends on surface coverage. Furthermore, the Tafel slope becomes pH-dependent when the coverage of intermediates changes with pH. These insights complicate the identification of a rate-limiting step by a single Tafel slope at a single pH. Yet, simulations of reaction orders complementary to Tafel slopes can solve some ambiguities to distinguish between possible rate-limiting steps. The most insightful information can be obtained from the low overpotential region of the Tafel plot. The simulations in this work provide clear guidelines to experimentalists for the identification of the limiting steps in the adsorbate mechanism using the observed values of the Tafel slope and reaction order in pH-dependent studies.

The electrochemical study of 2-Sulfanylidene-1,3-thiazolidin-4-one (rhodanine, R) was performed on a glassy carbon working electrode by using three methods: differential pulse voltammetry (DPV), cyclic voltammetry (CV), and linear sweep voltammetry (LSV) at rotating disk electrode voltammetry (RDE). The CV, DPV, and LSV at RDE curves for R were recorded at different concentrations in 0.1 M TBAP/CH₃CN. Polymeric films were formed by successive cycling at different potentials and by controlled potential electrolysis. The film formation was proved by recording the CV curves of the chemically modified electrodes (CMEs) in transfer solutions containing ferrocene in 0.1 M TBAP/CH₃CN. The obtained CMEs were used for the detection of heavy metal ions. Synthetic samples of heavy metal ions (Cd (II), Pb (II), Cu (II), Hg (II)) of concentrations between 10⁻⁷ and 10⁻⁵ M were analyzed using CMEs prepared in different conditions. The most intense signal was obtained for Pb(II) ion (estimated detection limit = 10⁻⁷ M), which shows that these CMEs can be used for Pb(II) ion detection. The ability of R to form complexes with Pb(II) ion was also tested by UV-Vis spectrometry. The obtained results showed the formation of Pb(II)R₂ as the most stable complex.

We investigated the oxygen evolution reaction (OER) activity changes of cobalt oxide (CoO_x) thin films on Ir(111) and Pt(111) substrates by repeated OER measurements in 0.1 M KOH. Atomic force microscopy and X-ray photoelectron spectroscopy analysis of the as-prepared CoO_x/Ir(111) and CoO_x/Pt(111) showed similar surface morphologies of the CoO_x thin films and almost the same OER overpotentials, which were estimated to be around 430 mV. However, after three OER measurements, the overpotential of CoO_x/Ir(111) decreased by 70 mV, whereas that of CoO_x/Pt(111) increased slightly. Structural analysis showed that CoO_x/Ir(111) revealed the island-like nanostructures of CoO_x dispersed on Ir(111) surface, accompanied by the generation of CoOOH. In contrast, for CoO_x/Pt(111), the Pt(111) substrate remains covered by the CoO_x thin film. The results suggest that the interaface at CoO_x (CoOOH) nano-islands and Ir(111) substrate are responsible for reducing the OER overpotential.

Based on the existing literature, active chlorine-mediated electrochemical oxidation has been extensively studied when Cl^‒ is added or Cl^‒ is already present in the water matrices, as well as when Cl^‒ is released from the target organic pollutants during their degradation. However, no attempts have been published concerning the fate and role of bromide (Br^‒) ions released during the anodic oxidation (AO) of organobromine compounds. Therefore, the AO of bromophenol blue dye (BPB) was investigated in a parallel plate flow reactor using a boron-doped diamond (BDD) anode. The effect of the applied current on the color removal efficiency and mineralization of BPB solution was examined and compared with AO of phenol red (PR) which has a similar molecular structure to BPB (but without Br) in order to understand the role of Br heteroatoms on the mineralization of BPB. Faster and higher mineralization and discoloration were achieved when treated with BPB solution compared to PR under similar experimental conditions. This behavior was associated with the electrogeneration of BrO^‒, from the heteroatom Br which is released as the bromide ion (Br^‒), during the degradation of BPB. The active bromine species are formed via direct and indirect oxidation approaches which were proposed based on ion chromatography and linear scanning voltammetry analysis.

The hydrogen evolution reaction (HER), the key reaction for electrocatalytic production of hydrogen, is of fundamental importance due to its simplicity yet is very important for renewable energy. Notwithstanding, Pt is still the main catalyst for this reaction, which is not practical for the industrial deployment of this technology owing to the high cost and scarcity of Pt. The successful synthesis of high entropy alloy (HEA) nanoparticles opens a new frontier for the development of new catalysts. Herein we investigate the design of a multinary noble metal-free HER catalyst based on earth-abundant elements Co, Mo, Fe, Ni, and Cu. Using a machine learning (ML) approach in conjunction with first-principles methods, we build a model that can rapidly compute the hydrogen adsorption energy on the alloyed surfaces with high fidelity. Within the large composition space of the CoMoFeNiCu HEA, a large number of alloy combinations are shown to optimally bind hydrogen with a high probability. Further, most of these alloy compositions are found stable against dissociation into intermetallics, and hence synthesizable as a solid solution, by virtue of a large mixing entropy compared to mixing enthalpy and a small lattice mismatch between the elements. This finding is partly consistent with recent experimental results that synthesized five different CoMoFeNiCu HEA compositions. Our study underscores the significant impact that computational modeling and ML can have on developing new cost-effective electrocatalysts in the nearly-infinite materials design space of HEAs, and calls for experimental validation.