Bipolar electrochemistry was described as a wireless electrochemical technique in which a conductive object immersed in an external electric field became polarized, enabling coupled redox reactions at opposite ends without direct electrical contact. The induced interfacial potential difference between the two poles of the bipolar electrode governed the thermodynamic feasibility of these reactions, while the spatial distribution of the applied electric field determined their localization along the bipolar electrode. As bipolar electrochemistry had extended beyond its early electrochemical engineering roots into materials processing, energy storage, electrocatalysis, and sensing, this review summarized its fundamental principles and expanding applications. The theoretical foundations, direct-current and alternating-current system configurations, and key operational variables were summarized and discussed. Quantitative modeling approaches and their current predictive limitations were also discussed, alongside comparisons with conventional electrochemical methods. Recent experimental progress across surface engineering, two-dimensional material exfoliation, energy-storage device integration, electrocatalysis, and sensing was then surveyed. Remaining challenges in controllability, yield, selectivity, and scale-up were discussed, with attention to opportunities for improved process control and closer integration between electrochemical modeling and experimentally measurable material outputs.
A cost-effective, nominally metal-free electrocatalyst was developed from petroleum coke (PC), a low-value refinery waste, for the oxygen evolution reaction in alkaline water electrolysis. Porous activated carbon was prepared by chemically etching PC with alcoholic potassium hydroxide (KOH) for varying durations (1, 1.5 and 2 h), followed by thermal treatment. Electrochemical investigations showed that etching time strongly influenced the electrochemical performance of the resulting carbons. Among the three catalysts, the sample etched for two hours (PC-2 h) exhibited the lowest overpotential, 68 mV at a current density of 10 mA cm⁻², and the smallest Tafel slope, 27.7 mV dec⁻¹, in 1.0 M KOH electrolyte. These results demonstrate the potential of converting a low-value petroleum refining by-product into an efficient electrocatalyst for clean-energy applications, supporting a waste-to-wealth approach to sustainable materials development.
Platinum-based electrocatalysts were the core materials for the cathodic oxygen reduction reaction in proton exchange membrane fuel cells, but their traditional carbon carriers suffered from serious issues such as severe electrochemical corrosion and poor structural stability, which severely limited the large-scale application of fuel cells. Therefore, the development of new platinum-based electrocatalysts with enhanced oxygen reduction reaction performance and excellent durability became a research focus in electrocatalysis. A composite carrier was constructed using multilayer titanium carbide MXene and high-surface-area Ketjen Black to load platinum nanoparticles, resulting in a three-dimensional platinum-based electrocatalyst for oxygen reduction reaction. The branched structure of Ketjen Black acted as a physical spacer within the MXene framework, effectively inhibiting the stacking and agglomeration of the MXene nanosheets; Meanwhile, the strong metal-support interaction between the composite support and platinum nanoparticles modified the local electronic environment of platinum, contributing to improved oxygen reduction reaction performance and enhanced durability. Oxygen reduction reaction measurements in a 0.1 M HClO4 electrolyte showed that the electrochemically active surface area of the catalyst reached 184 m² g⁻¹, which was 2.3 times that of commercial platinum on carbon. In addition, Pt/Ti3C2Tx-KB exhibited a mass activity of approximately 0.024 A mgPt⁻¹, together with improved electrochemical durability during long-term operation. After 30,000 cycles of accelerated durability testing, the electrochemically active surface area retention was about 86
As a lithiation method for graphite negative electrodes that avoids the use of highly reactive reagents such as lithium metal or strong reducing agents, the counter reaction for the intercalation of hexafluorophosphate ions (PF6–) in a graphite sheet was tested, and the conditions for the electrochemical lithiation process were examined. When using a 0.42-mm-thickness graphite sheet, a capacity of 1.5 mAh cm–2 (40 mAh g–1 based on the weight of the graphite sheet) was observed in the system with PF6– intercalation in the graphite sheet and lithiation in the negative electrode under constant current constant voltage charging conditions for 8 h. This PF6–-intercalated graphite sheet could be de-intercalated by immersion in water for 24 h at room temperature and reused for lithiation after drying. PF6– and its hydrolysis products such as PO3F2– were detected in the water used for immersing the graphite sheet after PF6– intercalation. After 5 cycles of lithiation and regeneration of the graphite sheet, no significant decrease in the capacity of lithiation was observed.
Cu₂O and CuO are common oxide precursors for preparing oxide-derived Cu electrodes in electrochemical CO₂ reduction. However, the relation between precursor phase, defect characteristics, reconstruction behavior and product distribution is still not fully clear. In this paper, we present a study of Cu-based electrodes prepared by anodic oxidation at different applied voltages. The phase structure, morphology, oxidation state, local coordination and open-volume defects of the samples were investigated by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, X-ray absorption spectroscopy (XAS) and positron annihilation spectroscopy (PAS). Our results show that the anodization voltage can control the phase evolution from Cu₂O-rich to CuO-rich electrodes. This phase change is accompanied by changes in local structural disorder and vacancy-related defects. XAS results show changes in Cu oxidation states and local Cu–O/Cu–Cu coordination, while PAS provides complementary information on open-volume defects. The PAS results are consistent with oxygen-vacancy-related trapping in the Cu₂O-rich electrode and suggest possible interfacial vacancy-related complexes in the mixed Cu₂O/CuO sample. In the CuO-rich electrode, an additional long-lived component indicates the presence of larger open-volume, nanopore-type defects. Electrochemical measurements show that different precursor electrodes give different product distributions at − 0.8 V vs. RHE. Bare Cu mainly gives H₂ and CO, Cu_0.75 V shows the highest CH₃COOH contribution, and Cu_1.0 V shows the highest HCOOH contribution in this sample series. However, the product selectivities are still modest and H₂ remains a competing product. Therefore, the role of the oxide precursor should be understood mainly in terms of its potential influence on reconstruction and product formation, rather than assuming that the initial oxide heterostructure remains unchanged during reaction. The inherited vacancy defects and possible dynamic Cu⁺/Cu⁰ species may contribute to this process. This study shows that the combination of XAS and PAS is useful for distinguishing defect environments in oxide-derived Cu electrodes and provides further insight into how oxide precursor phase and vacancy chemistry are associated with reconstruction behavior and CO₂RR product distribution.
