Anodic Reaction Research Articles

Sequential oxygen evolution and decoupled water splitting via electrochemical redox reaction of nickel hydroxides

Alkaline water electrolysis is a promising low-cost strategy for clean and sustainable hydrogen production but is largely limited by the sluggish anodic oxygen evolution reaction and the challenges in maintaining adequate separation between H2 and O2. Here, we reveal an anodic-cathodic sequential oxygen evolution process via electrochemical oxidation and subsequent reduction of Ni hydroxides, enabling much lower overpotentials than conventional anodic oxygen evolution. By using (isotope-labeled) differential electrochemical mass spectrometry and in situ Raman spectroscopy combined with density functional theory calculations, we evidence that the sequential oxygen evolution originates from the electrochemical oxidation of Ni hydroxides to NiOO– active species while undergoing a different, reductive step of NiOO– for the final release of O2 due to weakened Ni–O covalency. Based on this sequential process, we propose and demonstrate a hybrid water electrolysis and energy storage device, which enables time-decoupled hydrogen and oxygen evolution and electrochemical energy storage in the Ni hydroxides.

Valence Band-Tunable NiFe Electrocatalyst Triggered by the Dynamic Mo Exudation and Re-Deposition for Superior High Current Density Oxygen Evolution Reaction.

Developing energy- and time-efficient strategies to derive high-performance non-precious electrocatalysts for anodic oxygen evolution reaction (OER), especially stably working at industrial-demanding current density, is still a big challenge. In this work, a concise molten salt erosion scenario was devised to rapidly modulate the smooth surface of the commercial NiMo foam substrate into the rough, electronically coupled, and hierarchically porous Ni/Fe/Mo(oxy)hydroxide catalyst layer assembled by the nanosphere array. This self-supported catalyst is super-hydrophilic for the alkaline electrolyte and distinguished by a balanced Mo leaching/surface-readsorption process to tune the metal d band center and electronic perturbation. The altered electronic environment with the favored OER intermediate adsorption behavior attains the outstanding OER activity in terms of a very small overpotential of 230.21 mV at 10 mA cm-2 and an ultra-long stability for 1179.45 h to sustain the initial commercial-level current density of ca. 1000 mA cm-2. This superb performance transcends most of the edge-cutting transition metal peers reported recently and can satisfy the standards of industrial applications. This industrial-compatible synthesis technology holds profound implications for hydrogen production via water splitting and other electrochemical applications.

Redox-mediated decoupled seawater direct splitting for H2 production

Seawater direct electrolysis (SDE) using renewable energy provides a sustainable pathway to harness abundant oceanic hydrogen resources. However, the side-reaction of the chlorine electro-oxidation reaction (ClOR) severely decreased direct electrolysis efficiency of seawater and gradually corrodes the anode. In this study, a redox-mediated strategy is introduced to suppress the ClOR, and a decoupled seawater direct electrolysis (DSDE) system incorporating a separate O2 evolution reactor is established. Ferricyanide/ferrocyanide ([Fe(CN)6]3−/4−) serves as an electron-mediator between the cell and the reactor, thereby enabling a more dynamically favorable half-reaction to supplant the traditional oxygen evolution reaction (OER). This alteration involves a straightforward, single-electron-transfer anodic reaction without gas precipitation and effectively eliminates the generation of chlorine-containing byproducts. By operating at low voltages (~1.37 V at 10 mA cm−2 and ~1.57 V at 100 mA cm−2) and maintaining stability even in a Cl−-saturated seawater electrolyte, this system has the potential of undergoing decoupled seawater electrolysis with zero chlorine emissions. Further improvements in the high-performance redox-mediators and catalysts can provide enhanced cost-effectiveness and sustainability of the DSDE system.

Oxyanion Engineering on RuO2 for Efficient Proton Exchange Membrane Water Electrolysis.

In acidic proton exchange membrane water electrolysis (PEMWE), the anode oxygen evolution reaction (OER) catalysts rely heavily on the expensive and scarce iridium-based materials. Ruthenium dioxide (RuO2) with lower price and higher OER activity, has been explored for the similar task, but has been restricted by the poor stability. Herein, we developed an anion modification strategy to improve the OER performance of RuO2 in acidic media. The designed multicomponent catalyst based on sulfate anchored on RuO2/MoO3 displays a low overpotential of 190 mV at 10 mA cm-2 and stably operates for 500 hours with a very low degradation rate of 20 μV h-1 in acidic electrolyte. When assembled in a PEMWE cell, this catalyst as an anode shows an excellent stability at 500 mA cm-2 for 150 h. Experimental and theoretical results revealed that MoO3 could stabilize sulfate anion on RuO2 surface to suppress its leaching during OER. Such MoO3-anchored sulfate not only reduces the formation energy of *OOH intermediate on RuO2, but also impedes both the surface Ru and lattice oxygen loss, thereby achieving the high OER activity and exceptional durability.

Empowering Tri-Functional Palladium's Catalytic Activity and Durability in Electrocatalytic Formic Acid Oxidation Reaction via Innovative Self-Caging and Alloying Strategies.

Direct formic acid fuel cells (DFAFCs) stand out for portable electronic devices owing to their ease of handling, abundant fuel availability, and high theoretical open circuit potential. However, the practical application of DFAFCs is hindered by the unsatisfactory performance of electrocatalysts for the sluggish anodic formic acid oxidation reaction (FAOR). Palladium (Pd) based nanomaterials have shown promise for FAOR due to their highly selective reaction mechanism, but maintaining high electrocatalytic durability remains challenging. In this study, a novel Pd-based electrocatalyst (UiO-Pd-E) is reported with exceptional durability and activity for FAOR, which can be attributed to the Pd nanoparticles encapsulated within a carbon framework where concurrent chemical alloying of Pd and Zr occurs. Further, the UiO-Pd-E demonstrates noteworthy multifunctionality in various electrochemical reactions including electrocatalytic ethanol oxidation reaction (EOR) and oxygen reduction reaction (ORR) in addition to the FAOR, highlighting its practical potentials.

Recent development of non‐iridium‐based electrocatalysts for acidic oxygen evolution reaction

AbstractProton exchange membrane water electrolyser (PEMWE) possesses great significance for the production of high purity of hydrogen. To expedite the anodic oxygen evolution reaction (OER) that involved multiple electron–proton‐coupled process, efficient and stable electrocatalysts are highly desired. Currently, noble‐metal Ir‐based materials are the benchmark anode due to its corrosion‐resistant property and favourable combination of activity/stability. However, the large‐scale deployment of PEMWE is usually constrained due to the use of the scarcest element iridium. In this review, we disclose the current research progress towards the non‐iridium‐based electrocatalysts for OER in acidic media, and then summarize some typical oxides that possesses good catalytic performance. Besides, we also present the unresolved problems and challenges in an attempt to enhance the activity/stability of these catalysts.

Ultrafast Room-Temperature Synthesis of Phosphate-Intercalated NiFe Layered Double Hydroxides for High-Performance Alkaline Seawater Oxidation.

Quick and easy synthetic methods and highly efficient catalytic performance are equally important to anodic oxygen evolution reaction (OER) electrocatalysts for alkaline seawater electrolysis. Herein, we report a facile one-step route to in situ growing PO43- intercalated NiFe layered double hydroxides (NiFe-LDH) on Ni foam (denoted as NiFe-P/NF) by a room-temperature immersion for several minutes. This ultrafast approach transforms the NF surface into a rough PO43- intercalated NiFe-LDH overlayer, which demonstrates outstanding OER performance in both alkaline simulated and natural seawaters owing to good hydrophilic interface and the electrostatic repulsion of PO43- against Cl- anions. Density functional theory calculations reveal that the intercalated PO43- can not only promote electron transfer but also prevent Cl- from entering the interlayer and simultaneously inhibit the migration of Cl- over the NiFe-LDH surface. In alkaline simulated and natural seawater electrolytes, NiFe-P/NF needs low overpotentials of 248 and 298 mV to achieve a current density of 100 mA cm-2, respectively. NiFe-P/NF can stably run over 42 h in an alkaline high-salty electrolyte (1 M KOH + 2.5 M NaCl) at 250 mA cm-2, more than 70 times that of NiFe/NF (0.6 h), emphasizing the critical role of the intercalated PO43- anions on the excellent durability. This study offers a new strategy to modify commercial NF to prepare efficient and stable OER catalysts for seawater electrolysis.

Oxidative reconstructed Ru-based nanoclusters forming heterostructures with lanthanide oxides for acidic water oxidation

Achieving rapid anodic oxygen evolution reaction (OER) kinetics and improving the stability of the corresponding ruthenium (Ru)-based catalysts is a current priority for the realisation of industrial water splitting. However, the activity and stability of O2 evolution in electrocatalysis are largely inhibited by the insufficient adsorption of the reactant H2O and too strong adsorption of the intermediate OOH*, as well as by the dissolution of the active site due to excessive oxidation. To solve this challenge, herein, we developed a regulatory strategy combining lanthanide oxides and metal oxidative reconfiguration. The introduction of Eu2O3 effectively promotes the adsorption of H2O, optimizes the adsorption energy of OOH*, and reduces the reaction energy barrier of acidic OER process. And the metal oxidation remodeling process exposed more active sites and prevented the peroxidation process. The optimized Ru/Eu2O3@CNT catalyst showed the highest catalytic activity and stability in acidic OER. Its mass activity was 1219.1 A gRu−1 and the TOF value reached 4.4 s−1 at 1.48 V. Additionally, Ru/Eu2O3@CNT after oxidative reconstruction demonstrates the industrially needed current density of 1.0 A cm−2 at 1.71 V in PEM electrolyser, achieving stability in excess of 200 h.

Electrochemical, gravimetric and surface studies of Phalaris canariensis oil extract as corrosion inhibitor for 316 L type stainless steel in H2O-LiCl mixtures

The corrosion inhibition action of Phalaris canariensis extract on 316 L stainless steel in the H2O-35 (wt%) LiCl mixture at different temperatures has been evaluated with the aid of weight loss, potentiodynamic polarization curves, linear polarization resistance and electrochemical impedance spectroscopy tests. These studies were complemented by Fourier Transformed Infrared spectroscopy, FTIR, gas/mass chromatography analytical techniques and detailed scanning electronic microscopy studies. Results have indicated that Phalaris canariensis extract is an efficient inhibitor, with an efficiency that increases with its concentration, but it decreases as the temperature increases. Phalaris canariensis extract is physically adsorbed onto stainless steel according to a Temkin type of adsorption isotherm. Phalaris canariensis extract affected both anodic and cathodic electrochemical reactions with a stronger effect on the anodic ones, acting, thus, as a mixed type of inhibitor. Main compounds contained in the Phalaris canariensis extract were palmitic and oleic acids, responsible for its inhibitory properties.

Interfacial Acid‐Like Microenvironment and Orbital Modulating Strategy toward Efficient Hydrogen Evolution in Neutral High‐Salinity Wastewater/Seawater

Electrochemical high‐salinity wastewater splitting is a promising technology for green hydrogen (H2) production. However, the kinetics of hydrogen evolution reaction (HER) in neutral media is slow, and the high theoretical potential of oxygen evolution reaction leads to large energy losses. Herein, an iron‐based electrocoagulation‐coupled hydrogen production integrated system (IEHPS) is constructed, which is realized by coupling low‐potential anodic iron oxidation reaction with cathodic HER. The non‐noble metal HxWO3‐Ni catalyst is synthesized by fabricating a proton sponge HxWO3 to achieve an interfacial acid‐like microenvironment and doping it with Ni heteroatom to modulate the 4d orbital of W, thereby weakening the adsorption strength of the W site toward hydrogen. Consequently, the HxWO3 Ni demonstrates remarkable performance characteristics, boasting a mere 131 mV overpotential at 10 mA cm−2 and Tafel slope of 44 mV dec− in neutral media. Operating at an applied voltage of 1.5 V, the IEHPS exhibits a high hydrogen production rate of 235 mL g−1 min−1 in seawater. It achieves nearly complete removal of contaminants like rhodamine B and heavy metal ions within a rapid 8–20 min, with an energy consumption of only 3.7 kWh Nm−3. This study provides a promising pathway for efficient and energy‐saving production of high‐purity hydrogen and effective treatment of high‐salinity wastewater.

Regulating Zn2+ Migration-Diffusion Behavior by Spontaneous Cascade Optimization Strategy for Long-Life and Low N/P Ratio Zinc Ion Batteries.

Parasitic side reactions and dendrite growth on zinc anodes are formidable issues causing limited lifetime of aqueous zinc ion batteries (ZIBs). Herein, a spontaneous cascade optimization strategy is first proposed to regulate Zn2+ migration-diffusion behavior. Specifically, PAPE@Zn layer with separation-reconstruction properties is constructed in situ on Zn anode. In this layer, well-soluble poly(ethylene oxide) (PEO) can spontaneously separation to bulk electrolyte and weaken the preferential coordination between H2O and Zn2+ to achieve primary optimization. Meanwhile, poor-soluble polymerized-4-acryloylmorpholine (PACMO) is reconstructed on Zn anode as hydrophobic flower-like arrays with abundant zincophilic sites, further guiding the de-solvation and homogeneous diffusion of Zn2+ to achieve the secondary optimization. Cascade optimization effectively regulates Zn2+ migration-diffusion behavior, dendrite growth and side reactions of Zn anode are negligible, and the stability is significantly improved. Consequently, symmetrical cells exhibit stability over 4000 h (1 mA cm-2). PAPE@Zn//NH4 +-V2O5 full cells with a high current density of 15 A g-1 maintains 72.2 % capacity retention for 12000 cycles. Even better, the full cell demonstrates excellent performance of cumulative capacity of 2.33 Ah cm-2 at ultra-low negative/positive (N/P) ratio of 0.6 and a high mass-loading (~17 mg cm-2). The spontaneous cascade optimization strategy provides novel path to achieve high-performance and practical ZIBs.

Surface coating engineering of titanate anodes based on tannic acid-formaldehyde polymer chelating bismuth ions for advanced sodium-ion capacitors

As a battery-type anode material for sodium ion capacitors (SICs), titanate (H2Ti2O5·H2O, HTO) exhibits good rate capability due to its layered structure, easy to insert Na+ ions and low potential during sodium-ion storage. However, the structure is unstable due to the lattice distortion resulting from the irreversible embedment of Na+ in the process of sodium storage. So there is a significant mismatch between the dynamic reaction of the HTO anode and the capacitive cathode. Surface coating engineering is a useful strategy for stabilizing the HTO structure, which is critical for improving the kinetic response. In this work, a surface coating technique is designed to enhance the surface of HTO nanoarrays on titanium foil by using the oligomers of tannic acid formaldehyde polymer (TAF) chelated Bi3+ ions (Bi-TAF). As a binder-free anode, HTO coated with Bi-TAF (HTO@Bi-TAF) exhibits more excellent capacity (335.2 mA h g−1, 0.1 A g−1), rate capability (212.3 mA h g−1, 2.0 A g−1), and cycle stability (97 % capacity maintenance following 2000 cycles at 1.0 A g−1) than HTO and HTO coated with TAF (HTO@TAF). At the sweep rate of 1.0 mV s−1, the kinetic investigation reveals that the capacitance contribution of HTO@Bi-TAF is 86 %. The SICs exhibit a significant energy/power density (89.4 Wh kg−1/250 W kg−1). This work shows that the Bi-TAF polymer coating has a dual effect of rate capability improvement and structural protection on the prepared HTO. This results in a reasonable and effective surface coating strategy that provides outstanding rate capability and extended cycle performance of titanium-based anode materials for SICs.

Bismuth doping unlocks stability of copper oxides in anodic reaction: A case analysis of glucose electrooxidation

The instability of transition metal oxides during long-term electrolysis significantly impedes their application in various electrochemical reactions. This study demonstrates an interfacial doping strategy utilizing bismuth to enhance the stability of CuO catalyst during glucose electrooxidation in alkaline media. This methodology reduces activity decay from 55% to 6% after 8 h of electrolysis, lowering charge transfer resistance without compromising the intrinsic catalytic activity of the Cu sites. The enhanced stability can be attributed to the formation of a Cu−O−Bi interface on the catalyst surface, which mitigates the interfacial Cu dissolution, as evidenced by in situ electrochemical impedance analysis. These findings underscore the potential efficacy of bismuth doping strategies in advancing the development of robust and efficient catalysts for anodic catalysis. Furthermore, this research highlights the prospect of employing main group metals as dopants in transition metal oxides, thereby expanding the horizon of possibilities in catalyst design.

Vapor-feed direct methanol fuel cells using pure methanol

This work optimizes the performance of the direct methanol fuel cell (DMFC) to increase its efficiency and strengthen its validity in portable power generation. Specifically, this work focuses on optimizing vapor-feed supply techniques and incorporating water management layers (WMLs) to analyze their effect on methanol crossover. The significance of the vapor-feed supply technique is to enhance the reaction kinetics of the methanol oxidation reaction (MOR) and enable the use of pure methanol (MeOH) as a fuel. Pure methanol is the ideal fuel for the DMFC as it has the highest possible energy density compared to dilute concentrations. However, use of pure methanol is hindered by methanol crossover, which is regarded as the largest technical barrier to commercializing DMFCs. This study measured methanol crossover through a CO2 sensor attached to the cathode outlet and added hydrophobic WMLs to the cathode to alleviate the methanol crossover. The hydrophobic WMLs increased the mass transfer resistance to generate a pressure gradient that encourages water backflow for use in both the proton exchange membrane (PEM) and anode reactions. The influence of vapor flow rate and fuel concentration will also be explored to show their impact on performance and methanol crossover. Likewise, long-term consumption and durability tests were conducted with and without a WML to dictate the WML’s superior fuel efficiency, total efficiency, energy density, and reduced methanol crossover using pure methanol. The addition of the WML increased the energy density of the vapor feed DMFC, using pure methanol, from 705.9 Wh kgMeOH-1 to 867.7 Wh kgMeOH-1 and lowered the crossover current density by 14.8 % when discharged at a constant 200 mA cm−2.

Optimal Electrocatalyst Design Strategies for Acidic Oxygen Evolution.

Hydrogen, a clean resource with high energy density, is one of the most promising alternatives to fossil. Proton exchange membrane water electrolyzers are beneficial for hydrogen production because of their high current density, facile operation, and high gas purity. However, the large-scale application of electrochemical water splitting to acidic electrolytes is severely limited by the sluggish kinetics of the anodic reaction and the inadequate development of corrosion- and highly oxidation-resistant anode catalysts. Therefore, anode catalysts with excellent performance and long-term durability must be developed for anodic oxygen evolution reactions (OER) in acidic media. This review comprehensively outlines three commonly employed strategies, namely, defect, phase, and structure engineering, to address the challenges within the acidic OER, while also identifying their existing limitations. Accordingly, the correlation between material design strategies and catalytic performance is discussed in terms of their contribution to high activity and long-term stability. In addition, various nanostructures that can effectively enhance the catalyst performance at the mesoscale are summarized from the perspective of engineering technology, thus providing suitable strategies for catalyst design that satisfy industrial requirements. Finally, the challenges and future outlook in the area of acidic OER are presented.

Unlocking OER potential: Tailoring layered double perovskites through self-reconstruction

The sluggish rate of the anode oxygen evolution reaction (OER) is a major bottleneck for green hydrogen production, making a room-temperature alkaline water electrolyser critical to unlocking the full potential of this technology. Using a perovskite oxide as an electrochemical matrix and forming a self-assembled oxyhydroxide (OOH) layer on the surface via a self-reconstruction activation process (SRAP) is a promising strategy to enhance OER catalytic activity. However, the mechanistic details and long-term impact of SRAP, especially its relationship to catalytic activity, oxygen collection efficiency, and catalyst dissolution, are not fully understood. To address this knowledge gap, we used layered double perovskite (LDP) PrBa0·75Ca0·25Co1·5Fe0·5O5+δ(PBCCF) and PrBa0·75Ca0·25Co1·5Fe0·4Ni0·1O5+δ (PBCCFN) as model electrochemical catalysts and then triggered SRAP. Subsequently, chronoamperometry (CA), rotating ring disk electrode (RRDE) and in-situ electrochemical quartz crystal microbalance (EQCM) were used to study the effect of the Ni-doping on PBCCF SRAP in terms of catalytic activity, oxygen collection efficiency and catalyst stability. The results showed that the OER catalytic current of the LDP PBCCF and PBCCFN was enhanced via SRAP and the oxygen collection efficiency can be maintained, suggesting that the increase in catalytic current is attributed to OER catalytic activity increase rather than electrochemical catalyst dissolution. Additionally, the effect of the catalytic activity enhancement was more significant in PBCCFN. More importantly, the stability of the LDP PBCCF and PBCCFN after SRAP are higher than simple perovskite Ba0·5Sr0·5Co0·8Fe0·2O3-δ (BSCF) because of the increase in the redeposition rate. The observations suggest that using LDP PBCCF and PBCCFN as matrices followed by triggering SRAP can provide valuable insights for designing LDP based OER electrocatalysts.

Recent Research on Iridium-Based Electrocatalysts for Acidic Oxygen Evolution Reaction from the Origin of Reaction Mechanism.

As the anode reaction of proton exchange membrane water electrolysis (PEMWE), the acidic oxygen evolution reaction (OER) is one of the main obstacles to the practical application of PEMWE due to its sluggish four-electron transfer process. The development of high-performance acidic OER electrocatalysts has become the key to improving the reaction kinetics. To date, although various excellent acidic OER electrocatalysts have been widely researched, Ir-based nanomaterials are still state-of-the-art electrocatalysts. Hence, a comprehensive and in-depth understanding of the reaction mechanism of Ir-based electrocatalysts is crucial for the precise optimization of catalytic performance. In this review, the origin and nature of the conventional adsorbate evolution mechanism (AEM) and the derived volcanic relationship on Ir-based electrocatalysts for acidic OER processes are summarized and some optimization strategies for Ir-based electrocatalysts based on the AEM are introduced. To further investigate the development strategy of high-performance Ir-based electrocatalysts, several unconventional OER mechanisms including dual-site mechanism and lattice oxygen mediated mechanism, and their applications are introduced in detail. Thereafter, the active species on Ir-based electrocatalysts at acidic OER are summarized and classified into surface Ir species and O species. Finally, the future development direction and prospect of Ir-based electrocatalysts for acidic OER are put forward.

Doping-mediated interface engineered Ni3S2: Economically viable electrochemical methanol-mediated water splitting

Electrochemical water splitting is the front runner to meet the global green hydrogen demand. The development of a noble metal-free earth-abundant electrocatalyst is desired to rationalize an economically viable electrochemical water-splitting system. The sluggish anodic oxygen evolution reaction (OER) is the bottleneck of the electrochemical water-splitting system. Herein, to improve OER kinetics, group VIB elements such as chromium (Cr), molybdenum (Mo), and tungsten (W) doped nickel sulfides (Ni3S2) nanosheets (NSs) are synthesized by two-step hydrothermal method to modulate the intrinsic electrocatalytic activity of the pure Ni3S2. Among all the doped samples, the Cr-doped Ni3S2 catalyst exhibited excellent OER with an ultra-low overpotential of 248 mV and MOR with a potential of 1.36 V @ 10 mA cm−2 vs RHE achieving a lower Tafel slope of 95.5 mV/dec and 46.4 mV/dec and outstanding durability with negligible degradation respectively. Furthermore, the Pt/C||Cr-Ni3S2 (1.48 V) system outperforms commercial Pt/C||RuO2 (1.53 V @ 10 mA cm−2) in a two-electrode configuration. The methanol-mediated hybrid water splitting system only warranted a cell voltage of 1.38 V to attain 10 mA cm−2 for the Pt/C||Cr-Ni3S2 system in the presence of 0.1 M methanol (MeOH). The methanol oxidation reaction (MOR) mediated the hybrid water electrolyzer system demonstrates reduced operation cell voltage while additionally electro-synthesizing formate as a value-added chemical. The overall work is motivated to rationalize the importance of doping-mediated interface-engineered catalyst synthesis to improve the electrocatalytic efficiency of the hybrid water electrolyzer.

Corrosion protection of mild steel via cerium nitrate loaded acrylic-vinyl polysilazane based hybrid coatings

This study presents an efficient anticorrosive coating based on an organic-inorganic hybrid polymer composed of methyl methacrylate, styrene, tert-butyl acrylate, and vinyl polysilazane. The synthesized resin exhibits excellent thermal resistance and stability, as confirmed by thermogravimetric analysis (TGA). Additionally, leveraging the resin's highly alkaline nature, cerium oxide (CeO2) nanoparticles were doped in situ within the polymer matrix. The hybrid resins were subsequently applied to mild steel panels using a dip-coating technique. The resulting coatings are transparent, flexible, thin, pore-free, and possess low surface roughness (<2.62 nm), along with good thermal stability (>350 °C). Their remarkable anticorrosive performance and durability are attributed to forming a highly crosslinked acrylic-polysilazane network, combined with a cerium oxide protective barrier layer that adheres to the substrate. Furthermore, the cerium ions suppress both cathodic and anodic corrosion reactions, enhancing the corrosion resistance. Notably, the coating system containing 2 wt% cerium achieved a high impedance value of 106 Ω cm2, corresponding to a corrosion rate of 0.112 × 10−5 mm/year. This study demonstrates that these acrylic-vinyl polysilazane coatings, incorporating ceria as a corrosion inhibitor, offer a promising alternative to conventional protection systems.

Synthesis of a new quaternary ammonium salt for efficient inhibition of mild steel corrosion in 15 % HCl: Experimental and theoretical studies

The corrosion phenomenon and its economic impacts can hardly be ignored in any application. This study synthesized a quaternary ammonium salt (3) containing hydrophobic dodecyl and electron-rich diallylbenzyl amine moieties to be used in 15 % HCl as a corrosion inhibitor of mild steel. Several techniques, such as 1H and 13C NMR, IR, TGA, and elemental analysis, have been used to characterize inhibitor 3. Popular corrosion measurement techniques, namely weight loss, potentiodynamic polarization techniques, and electrochemical impedance spectroscopy, have been used to determine the efficiency of inhibitor 3. At 303 K and a moderately low concentration of 50 ppm, the quaternary ammonium salt-based inhibitor demonstrated a maximum efficiency of ≈95.0 %. At elevated temperatures of 313, 323, and 333 K, the inhibition efficacy values were recorded as 91.3, 82.8, and 75.0 %, respectively. Adsorption isotherm study revealed that the adsorption of inhibitor 3 followed Langmuir adsorption isotherm. The value of ΔGads° was found to be – 40.19 kJ mol−1, indicating that inhibitor 3 became adsorbed via a mixed physi-chemisorption mechanism. A very high adsorption constant (Kads) of 1.53 × 105 L mol−1 suggested strong adsorption of inhibitor 3. The difference in activation energy (Ea) value of 42.4 kJ mol−1 between the control and the inhibited solution indicated an efficient adsorption of inhibitor 3. The ability of inhibitor 3 to retard both anodic and cathodic half-cell reactions was proved via open circuit potential and Tafel curves studies. Detailed discussions on the change in corrosion current densities (icorr), polarization (Rp) and charge transfer (Rct) resistances have been offered to discuss the inhibition efficiency. Water contact angle measurement showed a drastic increase in mild steel surface hydrophobicity following inhibitor 3 adsorption. SEM-EDX and XPS studies confirmed the definitive presence of inhibitor 3 on the mild steel surface. Density functional theory (DFT) studies revealed the frontier molecular orbitals with which the metal surface interacts. A detailed corrosion inhibition mechanism has been offered in the context of adsorption isotherm and DFT studies.