High selective electrocatalytic reduction of carbon dioxide to ethylene enabled by regulating the microenvironment over Cu-Ag nanowires

Copper-based tandem catalysts are effective candidates for yielding multi-carbon (C2+) products in electrochemical reduction of carbon dioxide (CO2RR). However, these catalysts still face a significant challenge regarding in the low selectivity for the production of a specific product. In this study, we report a high selectivity of 77.8 %±2 % at -1.0 V (vs RHE) for the production of C2H4 by using a Cu88Ag12NW catalyst which is primarily prepared through a combined Cu-Ag co-deposition and wet chemical method, employing an attractive strategy focused on regulating the microenvironment over Cu-Ag nanowires. The experimental and computational studies show that the higher *CO coverage and lower intermediate adsorption energy are important reasons for achieving the high C2H4 selectivity of Cu88Ag12NW catalyst. Comsol simulation results indicate that dense nanowires exhibit a nano-limiting effect on OH- ions, thereby leading to an increase in local pH and promoting coupling reactions. The catalyst demonstrates no noticeable decrease in current density or selectivity even after 12 h of continuous operation. The Cu-Ag nanowire composite exhibits remarkable catalytic activity, superior faradaic efficiency, excellent stability, and easy synthesis, which highlights its significant potential for electro-reducing carbon dioxide into valuable products.

Basket anode filled with CaCO3 particles: A membrane-free electrochemical system for boosting phosphate recovery and product purity

Phosphorus (P) is often regarded as the primary stimulant for eutrophication, while its importance as a crucial life element is also well acknowledged. Given its future scarcity, P recycling from waste streams is suggested and practiced. Electrochemically mediated precipitation (EMP) is a robust and chemical-free process for P removal and recovery, yet it requires further developments. The first generation of the CaCO₃-packed electrochemical precipitation column successfully solved the problem of H⁺-OH^- recombination, achieving enhanced P removal efficiency with less energy consumption but suffering from low Ca-phosphate purity in recovered products. Herein, a new concept of a basket-anode electrochemical system is proposed and validated to prevent direct H⁺-OH^- recombination and enhance product purity. The CaCO₃ pellets packed basket anode alleviates the OH^- depletion by CaCO₃-H⁺ interaction and provides extra Ca²⁺ for enhanced P removal. The novel structure of the basket anode, by its derived acidic anode region and alkaline cathode region, completely avoids the precipitation of Ca-phosphate on the packed CaCO₃ and greatly facilitates the collection of high-quality Ca-phosphate product. Our results suggest that almost 100% of the removed P was in high-purity, highly crystalline Ca-phosphate on the cathode. The recovered products contained significantly more P (13.5 wt%) than in the previous study (0.1 wt%) at similar energy consumptions (29.8 kWh/kg P). The applied current density, pellets size, and influent P concentration were critical for P removal performance, product purity, and power consumption. We further demonstrated the long-term stability of this novel system and its technical and economic feasibility in treating real stored urine. Our study provides new cell architectural designs to enhance the performance of EMP systems and may inspire innovations and developments in other electrochemical water treatment processes.

Biodegradation behaviour of Fe-based alloys in Hanks' Balanced Salt Solutions: Part II. The evolution of local pH and dissolved oxygen concentration at metal interface

Commercially pure Fe, Fe35Mn, and (Fe35Mn)5Ag alloys were prepared by uniaxial pressing of the mixture of individual powders, followed by sintering. The influence of the alloying elements Mn and Ag on the corrosion behaviour of these Fe-based alloys was investigated in Hanks' Balanced Salt Solution (HBSS). Furthermore, the role of the components in HBSS, particularly Ca2+ ions during alloys degradation was studied. Distribution of local pH and dissolved oxygen concentration was measured 50 μm above the interface of the degrading alloys. The results revealed that 5 wt% Ag addition to Fe35Mn alloy triggered micro-galvanic corrosion, while uniform corrosion dominated in pure Fe and Fe35Mn. Fast precipitation of Ca-P-containing products on the surface of these Fe-based alloys buffered local pH at the metal interface, and blocked oxygen diffusion at the initial stages of immersion. In the (Fe35Mn)5Ag, the detachment or structural changes of Ca-P-containing products gradually diminished their barrier property. These findings provided valuable insights into the degradation mechanism of promising biodegradable Fe-based alloys.

Biodegradation behaviour of Fe-based alloys in Hanks' Balanced Salt Solutions: Part I. material characterisation and corrosion testing

Research on Fe-based biodegradable alloys for implant applications has increased considerably over the past decade. However, there is limited information on the influence of testing electrolytes on corrosion product formation and general corrosion progress. In this work, the effect of Hanks' Balanced Salt Solution (HBSS) with or without Ca2+ on the corrosion of Fe, Fe35Mn and (Fe35Mn)5Ag powder-processed coupons has been studied using potentiodynamic polarisation, Electrochemical Impedance Spectroscopy (EIS), and preliminary localised measurement of pH and dissolved oxygen concentration in close proximity to the metal surface. Both Fe35Mn and (Fe35Mn)5Ag alloys showed accelerated corrosion when compared to pure Fe based on potentiodynamic testing results, with FeMnAg exhibiting the highest corrosion rate in Ca2+-containing HBSS. The results indicate that in Ca2+-containing HBSS, the formation of a partially protective Ca/P layer decelerates the corrosion progress, whereas the Fe- and Mn-phosphates formed in Ca2+-free HBSS do not have the same effect. The Ca/P layer on (Fe35Mn)5Ag experienced a reduction in resistance following several hours of testing, indicating partial loss of its protective effect.

Study on nanoporous CuBi2O4 photocathode coated with TiO2 overlayer for photoelectrochemical CO2 reduction

Investigation on the electrode/electrolyte interface of nanotextured electrodes is very challenging but critical to understand the CO₂ reduction reactions. Here we present that the nanoporous CuBi₂O₄ photocathodes coated by a TiO₂ overlayer with gradient thickness show improved CO₂ reduction performance compared to pristine CuBi₂O₄. Different activity and selectivity for photoelectrochemical CO₂ reduction are observed when the thickness of TiO₂ coating layer is set at two extreme values, i.e., less and longer than its Debye length. The CuBi₂O₄ with a thin TiO₂ layer shows higher CO/H₂ yield ratio, and the one with a thick layer exhibits lower CO/H₂ ratio but higher yield for both CO and H₂. All these are elucidated based on the results of Mott-Schottky plots, photocurrent response and SEM/TEM images. Results indicate that the TiO₂ overlayer on CuBi₂O₄ is in favor of the generation and separation of electron/hole pairs, and thus facilitate CO and H₂ production, while the nanoporous structure and the nonuniform TiO₂ overlayer on CuBi₂O₄ have a great impact on mass transport, local pH, and exposed active sites and, thereby, on the CO production selectivity.

Electrochemical removal of phosphate in the presence of calcium at low current density: Precipitation or adsorption？

Phosphorus removal and recovery from waste streams are crucial to prevent eutrophication and sustain fertilizer production. As has been shown in our previous papers, electrochemical treatment has the potential to achieve this goal. However, the adoption of electrochemical approach is limited by its high energy consumption. Here, we investigate the possibility of electrochemical phosphorus removal at extremely low current density using graphite felt as the cathode. We found a current density as low as 0.04 A/m² can enhance the removal of phosphate in our electrochemical system. The removal of phosphate at extremely low current density resulted from electrochemical induced calcium phosphate precipitation and not by electrochemical adsorption. Electrochemical treatment of real domestic wastewater at 0.2 A/m² almost eliminates the precipitation of Mg(OH)₂ and limits the formation of CaCO₃. The recovered precipitates are dominated by calcium phosphate (59%), followed by 35% CaCO₃ and 6% Mg(OH)₂. The specific energy consumption of this newly electrochemical system is between 4.4 and 26.4 kW h/kg P, which is 2 orders of magnitude lower than our previous system (110-2238 kW h/kg P). Key factors for this improvement prove to be enlarged precipitation area and hydroxide flux retardation by graphite felt. Practically, our study offers a potential way to reduce the energy consumption in electrochemical removal of phosphate by using a graphite felt cathode and at a current density below 0.2 A/m². Fundamentally, our study contributes to the understanding of adsorption and precipitation in electrochemical removal of phosphate at an extremely low current density and with carbon-based electrodes.

In vitro measurement of the chemical changes occurring within β-tricalcium phosphate bone graft substitutes

Several mechanisms proposed to explain the osteoinductive potential of calcium phosphates involve surface mineralization ("bioactivity") and mention the occurrence of concentration gradients between the inner and the outer part of the implanted material. Determining the evolution of the local chemical environment occurring inside the pores of an implanted bone graft substitute (BGS) is therefore highly relevant. A quantitative and fast method was developed to measure the chemical changes occurring within the pores of β-Tricalcium Phosphate (β-TCP) granules incubated in a simulated body fluid. A factorial design of experiment was used to test the effect of particle size, specific surface area, microporosity, and purity of the β-TCP granules. Large pH, calcium and phosphate concentration changes were observed inside the BGS and lasted for several days. The kinetics and magnitude of these changes (up to 2 pH units) largely depended on the processing and properties of the granules. Interestingly, processing parameters that increased the kinetics and magnitude of the local chemical changes are parameters considered to favor calcium phosphate osteoinduction, suggesting that the model might be useful to predict the osteoinductive potential of BGSs. STATEMENT OF SIGNIFICANCE: Recent results suggest that in situ mineralization of biomaterials (polymers, ceramics, metals) might be key in their ability to trigger ectopic bone formation. This is the reason why the effect on in situ mineralization of various synthesis parameters of β-tricalcium phosphate granules was studied (size, microporosity, specific surface area, and Ca/P molar ratio). To the best of our knowledge, this is the first article devoted to the chemical changes occurring within the pores of a bone graft substitute. We believe that the manuscript will prove to be highly important in the design and mechanistic understanding of drug-free osteoinductive biomaterials.

Determination of Local pH Differences within Living Salmonella Cells by High-resolution pH Imaging Based on pH-sensitive GFP Derivative, pHluorin(M153R)

The bacterial flagellar type III protein export apparatus is composed of a transmembrane export gate complex and a cytoplasmic ATPase complex. The export apparatus requires ATP hydrolysis and the proton motive force across the cytoplasmic membrane to unfold and transport flagellar component proteins for the construction of the bacterial flagellum (Minamino, 2014). The export apparatus is a proton/protein antiporter that couples the proton flow with protein transport through the gate complex ( Minamino et al., 2011 ). A transmembrane export gate protein, FlhA, acts as an energy transducer along with the cytoplasmic ATPase complex ( Minamino et al., 2016 ). To directly measure the proton flow through the FlhA channel that is coupled with the flagellar protein export, we have developed an in vivo pH imaging system with high spatial and pH resolution ( Morimoto et al., 2016 ). Here, we describe how we measure the local pH near the export apparatus in living Salmonella cells ( Morimoto et al., 2016 ). Our approach can be applied to a wide range of living cells. Because local pH is one of the most important parameters to monitor cellular activities of living cells, our protocol would be widely used for diverse areas of life sciences.