Journal of Solid State Electrochemistry最新文献

Herein, we prepared poly(heptazine imide) (PHI), a layered structure of carbon nitride material containing sodium cations that were later exchanged, allowing us to obtain single-atom catalyst (SAC) sites of nickel, cobalt, and iron. In addition, combinations among these metals (NiCo, NiFe, and CoFe) were evaluated as dual single-atom catalysts (DSAC). The samples containing transition metal presented a photocurrent response far superior to the unmodified Na-PHI. The maximum photocurrent obtained was for the sample NiCo-PHI in alkaline media, being ~ 70 µA cm⁻² at 1.2 V vs. RHE; this value was higher than both Ni-PHI and Co-PHI combined, indicative of a cooperative effect in the DSAC sample. Lastly, all samples containing transition metal, when studied in acidic media, presented both cathodic and anodic photocurrent indicating a bifunctionality potential for application in both reduction and oxidation of water.

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Contact angles of liquid, spherical cap droplets immobilised on an electrode surface and bathed by a fluid are important, quantifiable measures of the liquid/fluid interfacial tension. Optical goniometry, even if computer assisted, suffers when the contact angle is 10° or less. In this work, an alternative method of measurement is considered: electrochemical techniques (voltammetry and chronoamperometry), which rely on the transport of material from within the droplet to the conductive surface. As a result of the reactions that take place at the triple phase boundary, these are demonstrated to provide information on the size and the shape of the droplet, including its contact angle, for the cases when the droplets have a redox analyte and either have a supporting electrolyte, or not. The voltammetric behaviour is seen to change from exhaustive, thin film characteristics, to quasi-steady-state signals as the droplet becomes bigger, or the scan rate becomes larger, or diffusion of the redox material inside the droplet becomes slower. One of the surprising outcomes is that there is a zone of planar diffusion only in the case of the supported droplets, with both the droplet size and its contact angle determining whether this is seen at conventional combinations of scan rates and diffusion coefficients. Experimental data are provided which emphasize key features pertaining to the nature of the redox system and illustrate the facile nature of the contact angle estimation process, albeit to within 10% uncertainty.

Solid oxide fuel cell (SOFC) with high conversion efficiency has drawn great attention for a sustainable future. Its electrolyte, typically yttria-stabilized zirconia (YSZ), is usually sintered above 1400 °C with commercially available powder materials. To lower the sintering temperature, yttria-doped bismuth oxide (YDB) is investigated in this work as an additive to form composite electrolytes. Dilatometric analysis reveals that the temperature corresponding to the maximum shrinkage rate is decreased from 1260 to 870 °C by YDB. Meanwhile, adding YDB results in the formation of poor conductive second phase monoclinic zirconia (m-ZrO₂), especially when YDB content reaches 3 mol%. Thus, total conductivity decreases and then increases with YDB content. It is noted that the grain boundary conductivity is substantially improved, which is caused by bismuth enrichment at the grain boundary region of the dense composite electrolyte.

The electrochemical promotion of nano-sized Pd catalysis deposited on yttria-stabilized zirconia (YSZ) solid electrolyte (Pd/YSZ) was studied for complete methane oxidation in excess of oxygen. The as-prepared and used Pd/YSZ catalysts were characterized using TEM, SEM, and XRD techniques. In this study, for the first time, we demonstrated the electrochemical promotion of complete methane oxidation over Pd at temperatures as low as 300 °C. The electrochemical promotion of Pd/YSZ was carried out at different cathodic and anodic polarization values in excess of oxygen (p_O2 = 6 kPa) in temperatures ranging from 300—420 °C. Upon anodic and cathodic polarization the highest rate increase of 17.7 and 1.4 was observed at 420 °C, respectively. Chronoamperometric rate transients showed continuous rate increase with the polarization time indicating continuous activation of Pd/YSZ and formation of PdO_x active phase. When polarization was stopped the reaction rate slowly returned to its initial state showing the persistent EPOC, i.e., the open-circuit reaction rate after polarization was enhanced compared to initial open-circuit conditions (γ = 1.6 after 29 h of polarization). The changes occurring in the Pd catalyst during the polarization were studied using electrochemical techniques, such as cyclic voltammetry, steady-state polarization and electrochemical impedance spectroscopy (EIS).

Graphical Abstract

LiNi_0.8Co_0.1Mn_0.1O₂ (NCM811) cathode material is prized in the electric vehicles (EVs) industry for its high capacity and voltage during operation. However, the high residual alkali content and inferior ionic conductivity of Ni‑rich cathode materials are the intractable obstacles to the large-scale commercial application for a long time. Herein, a feasible Nb₂O₅ coating strategy is proposed to eliminate residual alkali along with constructing high Li⁺ conductive coating layer on NCM811 cathode materials surface. Impressively, 0.3% Nb₂O₅‑coated NCM811 cathode exhibits superior rate capability (146.4 mA h g⁻¹@400 mA g⁻¹) and remarkable rate cyclic stability (188.5 mA h g⁻¹ after 100 cycles with capacity retention of 94.8%). On the one hand, a small quantity of Nb₂O₅ coating on NCM811 surface can react with surface residual alkali to promote the transformation of low electronic conductivity surface residual alkali into the Li⁺ conductor of LiNbO₃ coating layer, enhancing Li⁺ de-intercalation kinetics and rate performance. On the other hand, excessive Nb₂O₅ coating may introduce Nb⁵⁺ into the lattice of NCM811, acting as pivotal components within the Li⁺ layer, which effectively suppresses the H2 ↔ H3 phase transition, contributing to long-term cyclic stability. This work paves a new path for the rational design and facile coating of Ni-rich oxide cathode materials with reinforced structure stability and boosted rate capability in high‑energy‑density lithium-ion batteries.

Nitrogen-doped graphene (N-graphene) electrocatalysts prepared using a thermal treatment procedure were systematically investigated for the oxygen reduction reaction (ORR). A central composite experimental design (CCD) was adopted to evaluate the effect of the thermal treatment temperature (from 660 to 940 °C) and mass ratio of graphene and urea precursors (from 1:3 to 1:17) on the electron transfer number (n) of the ORR in alkaline medium. No interaction effect was observed between the two factors, and only temperature had a positive and statistically-significant effect on the n value. XPS results indicated that the improvement of the electrocatalytic activity of N-graphene with the increase of doping temperature cannot be associated with the N configuration or the overall N content, but is related to the formation of defects on graphene. This investigation represents an important step in the adoption of multivariate experimentation for the exploration of metal-free electrocatalysts for fuel cell cathodes.

The present work investigates the properties of copper, being obtained by electrochemical 3D printing. The square copper object of 200 µm thickness was obtained from copper sulphate electrolyte. The mechanical and corrosion properties of the copper were investigated and compared to the galvanic and metallurgical copper. The Meier microhardness, Young’s modulus, and plasticity coefficients of electrochemically deposited copper correspond to the properties of 3D-printed copper within 5% accuracy. The linear polarization resistance technique, used in 3.5% NaCl solution, showed that the corrosion rate of printed copper (7.4 mA/cm²) lies in between the corrosion rate of metallurgical copper (11.1 mA/cm²) and the corrosion rate of galvanic copper (6.9 mA/cm²). Thus, the quality of the copper metal, obtained by 3D printing, remains the same as for traditional manufacturing making electrochemical printing a promising technology for copper parts production.