This study aimed to investigate the electrochemical behavior of the antidepressant sertraline (SER) in aqueous electrolytes over a wide range (pH = 3.10-9.33), on electrochemically pre-treated carbon electrodes (eCE), glassy carbon electrodes (eGCE), and screen-printed carbon electrodes (eSPCE). These studies were conducted using cyclic voltammetry (CV), square wave voltammetry (SWV), and differential pulse voltammetry (DPV), exploring different experimental conditions, such as the nature and pH of the supporting electrolyte, SER concentration, successive scans for identification and quantification of electroactive products of the identified electrochemical reactions of SER, CV scan rate for investigating the mass transport of SER to the electrode surface, and the influence of the carbon working electrode on the electrochemical response and surface adsorption. Electrochemical data indicated that SER was electrooxidized in aqueous media at high potential values, from an irreversible anodic reaction, controlled by diffusion, with the removal of one electron and one proton from its secondary amine and with the formation of an electroactive product. A mechanism of the electrooxidation of SER in aqueous medium, on carbon electrodes, was discussed and proposed. From the CV data, the diffusion coefficient of SER was established, DSER = 3.26 & times; 10-5 cm2 s- 1. A simple, sensitive, selective, and low-cost electroanalytical method for the determination of SER, using DPV and eGCE, was proposed. The analytical data allowed a concentration range of 0.50-8.53 mu mol L- 1, a limit of detection (LOD) of 0.34 mu mol L- 1, and a limit of quantification (LOQ) of 1.16 mu mol L- 1, with an average recovery of 93.0%. The proposed method was used for rapid determination or rapid screening of SER in samples of dietary supplements for weight loss.
The effect of carboxylate chain length on the corrosion behavior and discharge performance of Mg anodes in KNO3-based electrolytes is investigated using propionic acid (PA) and polyacrylic acid (PAA) with different molecular weights (2000 and 100,000 g & sdot;mol- 1). The results show that corrosion inhibition strongly depends on polymer chain length, with PAA-2000 exhibiting optimal performance, while PA provides limited protection and PAA-100000 leads to deteriorated behavior. Electrochemical measurements reveal increased Rct and Rf values for PAA-2000, accompanied by suppressed hydrogen evolution and improved discharge stability, whereas PAA100000 shows accelerated degradation. Surface analyses, including post-discharge characterization, indicate that chain length regulates the formation and spatial uniformity of Mg(OH)2/carboxylate-containing organic-inorganic interfacial layers. PAA-2000 promotes more homogeneous Mg dissolution and a regulated interfacial film during discharge, whereas excessively long PAA induces heterogeneous surface reactions, localized Mg exposure, and premature discharge degradation. Consistent trends observed in both nitrate- and chloride-based electrolytes suggest that the chain-length-dependent behavior is mainly governed by intrinsic carboxylate-Mg interfacial interactions, including adsorption and Mg2+ coordination, although electrolyte-dependent corrosionproduct chemistry may affect the quantitative response.
The commercialization of lithium-sulfur batteries is limited by the shuttle effect and the sluggish conversion of lithium polysulfides (LiPSs). The modification of conventional separator is an effective way to solve these problems. In this paper, a novel multistage porous NiCe@PPy composite was successfully prepared by using Ni-Ce bimetallic doped MOF as the main body and wrapping a layer of polypyrrole (PPy) using the ice bath. The prepared NiCe@PPy slurry was then coated on the separator. The nanoparticles of Ni-Ce bimetallic are able to strongly synergistically adsorb and catalyze the conversion of LiPSs. After encapsulating PPy, it possesses higher conductivity with lithophilic interfacial, which can effectively reduce the overpotential, ensure uniform lithiumion deposition, and suppress the generation of lithium dendrites. The lithium-sulfur batteries (LSBs) with this separator showed an initial discharge-specific capacity of 1585 mAhg- 1 at 0.2C, a high retention of 883 mAh g- 1 after 100 cycles, and a reversible capacity of 1388 mAh g- 1 at 1C.
Heavy metal contamination in drinking water is a critical global issue, as even trace levels pose serious health risks. Numerous studies report concentrations of heavy metals exceeding limits set by the WHO and the US-EPA. Electroanalytical sensing technologies have therefore gained importance for rapid, sensitive, and on-site detection of heavy metals. In this work, we present a scalable and industrially viable carbon nanotubes (CNT) film electrode for electrochemical detection of Pb2+ in water. The CNTs grown via chemical vapor deposition were uniformly press-transferred onto PET substrates to create carbon nanotube network thin films (CNT-NTF). This fabrication strategy enables large-area, reproducible, and mass-producible electrodes, addressing a major gap in earlier CNT-based sensors. CNT-NTF sensors achieved sub-nanomolar (ppb) detection limits for Pb2+, with two well-defined linear response ranges and reliable performance across buffer, simulated drinking water, tap water, and river water matrices. The electrode detected Pb2+ at concentrations significantly below WHO and US-EPA limits, while maintaining stable responses across temperatures from 5 to 45 degrees C. Interference studies confirmed robust detection in the presence of As3+ and Cd2+. The combination of low detection limits, stability in realworld samples, and compatibility with large-area fabrication highlights the CNT-NTF platform as a promising route toward scalable and cost-effective monitoring of heavy-metal contamination in water systems.
Impedance-based biosensing is a label-free electrochemical approach that detects biological targets by measuring frequency-dependent impedance responses at the electrode-electrolyte interface. Electrochemical impedance spectroscopy (EIS) provides spectra that reflect charge transfer, double-layer charging, interfacial adsorption, and mass transport, supporting applications in medical diagnostics, pathogen detection, food safety, and complex biosensing environments. However, practical deployment remains limited by drift, biofouling, electrode and batch variability, matrix interference, and dependence on expert-driven equivalent-circuit fitting and manual interpretation. This review examines how artificial intelligence (AI) can address these limitations by enabling automated feature learning, robust pattern recognition, full-spectrum interpretation, and direct prediction of analyte identity, disease state, or concentration from impedance measurements. Supervised learning for classification and regression is discussed alongside unsupervised methods for dimensionality reduction and clustering, as well as deep learning (DL) models that learn hierarchical representations from raw spectra and time-series data. Hybrid and transfer-learning strategies are highlighted for improving generalization under limited labeled data and variable sensing conditions. The review distinguishes raw-spectrum approaches from fittedparameter workflows, emphasizing differences in expert dependence, interpretability, accessibility, and practical implementation. Key preprocessing practices are analyzed, including feature extraction, normalization, scaling, denoising, model-independent spectral representation, and automated quality control for real-time pipelines. Validation strategies reflecting realistic electrochemical variability, including cross-electrode, crossbatch, and cross-day testing, are emphasized to support reproducibility across instruments and laboratories. Applications are highlighted across biomedical diagnostics, pathogen detection, food safety, and biosensor performance monitoring. Finally, translation challenges are discussed, including dataset standardization, interpretability, edge deployment, privacy, and regulatory considerations for deployable biosensing systems.
Electrochemical conversion of organic molecules coupled with green hydrogen (H2) production using renewable energy offers an opportunity for a zero-carbon emission energy economy. The development of the advanced electrocatalyst for energetically favorable benzyl alcohol electrooxidation reaction (BAOR) over the sluggish oxygen evolution reaction (OER) has emerged as an alternative route for the conventional water electrolyzer. In this study, we synthesized Ni(OH)2 nanoplates (NPs) decorated graphitic carbon nitride (Ni(OH)2/g-C3N4) catalyst by a wet chemical process and explored it as an efficient electrocatalyst for BAOR. In-situ potentialdependent electrochemical spectroscopy demonstrated efficient BAOR kinetics on the Ni(OH)2/g-C3N4 catalyst compared to the OER at the catalyst surface. The synergistic cooperation of the Ni(OH)2 NPs and g-C3N4 heterojunction offers abundant active sites for BAOR is validated by the density functional theory (DFT) calculations, which confirmed energetically preferable BAOR compared to OER, is consistent with the lower energy barriers observed for BAOR relative to the OER, which perfectly aligns with experimental observations. Moreover, a two-electrode electrolyzer is assembled using Ni(OH)2/g-C3N4 as an anode and Pt-sheets as a cathode to demonstrate simultaneous H2 production and benzyl alcohol electrooxidation.
Accurate spatial mapping of biomolecules in complex biological systems is essential for advancing diagnostics and understanding disease mechanisms. Traditional imaging methods, while powerful, often lack the capability to provide quantitative electrochemical information with high spatial resolution. Scanning electrochemical microscopy (SECM) addresses these gaps by enabling detailed, label-free, non-optical quantitative mapping from single cells to whole organs. This review focuses on SECM as a transformative tool in biological imaging, particularly through enzyme-assisted, label-free techniques for detecting proteins, metabolites, cytokines, and nanomaterials. We detail key operational modes, including feedback, generation-collection, redox competition, potentiometric, and dual-electrode approaches, and highlight core applications, including enzymatic amplification with alkaline phosphatase and horseradish peroxidase, aptamer-based detection, and oxidase-driven metabolite mapping. Recent advances, including single-cell receptor imaging, label-free metabolic profiling, integration with microfluidics, and soft-probe technologies that enable high-resolution imaging from single cells to tissues and whole organs, are discussed. Current challenges, including probe miniaturization, signal specificity, and data interpretation in heterogeneous systems, are critically discussed, along with future directions toward multiplexed detection and clinical translation. Overall, SECM represents a promising approach for next-generation biosensing and electrochemical imaging, bridging the gap between molecular recognition and functional biological analysis.
In this work, a tetrameric compound synthesized via direct (hetero)-arylation methods based on perylene diimide (PDI) end groups with fused thiophene cores, (PDI)4ThTh, which is a graphene-like compound with atomic precision, was investigated for electrochemiluminescence (ECL) and chemiluminescence (CL) applications. ECL performance and its absolute efficiencies of (PDI)4ThTh are determined with tri-n-propylamine (TPrA) or benzoyl peroxide (BPO) as coreactants. ECL-voltage curves along with spooling ECL spectra offered details of light generation mechanisms. CL emission of (PDI)4ThTh is explored for the first time in the chemical reaction with bis(2-carbopentyloxy-3,5,6-trichlorophenyl) oxalate (CPPO) and hydrogen peroxide (H2O2). Spooling CL spectroscopy is utilized for investigation of its CL reaction mechanism, illuminant decay and the absolute CL efficiency. Both ECL and CL emission peak wavelengths of (PDI)4ThTh correspond well to its photoluminescence (PL) one, demonstrating that ECL and CL emissions are mainly from the monomeric excited state in the absence of surface states. Therefore, the absolute ECL efficiencies are higher than that of N-annulated PDI dimers. Meanwhile, the absolute CL efficiency of (PDI)4ThTh is superior to that of many other organic molecules and graphene quantum dots. This work opens the door for the exploration of these PDI materials to improve the ECL and CL performances.
In this study, a new class of phthalazinone-triazole derivatives was rationally designed and synthesized using an eco-friendly click-chemistry approach to develop efficient and sustainable corrosion inhibitors for mild steel in acidic media. The chemical structures of the synthesized compounds were unambiguously confirmed by 1 H/ 13 C NMR spectroscopy and high-resolution mass spectrometry. Their corrosion inhibition performance was systematically investigated in 1 M HCl using electrochemical techniques, including open-circuit potential, potentiodynamic polarization, and electrochemical impedance spectroscopy. Electrochemical results revealed that all compounds act as highly effective mixed-type inhibitors, significantly reducing both anodic metal dissolution and cathodic hydrogen evolution reactions. At an optimal concentration of 10 -4 M, inhibition efficiencies exceeding 97% were achieved, accompanied by a pronounced increase in charge-transfer resistance and the formation of a compact, protective adsorbed film on the steel surface. To gain molecular-level insight into the inhibition mechanism, comprehensive multiscale theoretical investigations were performed using DFT, conceptual DFT, Monte Carlo, and molecular dynamics simulations. Theoretical results demonstrated strong and stable adsorption of the inhibitors on the Fe(110) surface through multiple Fe - N, Fe - O, and Fe - C interactions, in excellent agreement with experimental observations. Adsorption thermodynamics followed the Langmuir isotherm model, confirming spontaneous chemical adsorption.
In this study, a FeTi/CNT (FeTi/C-350) nanomaterial was prepared via pyrolysis of pre-treated PVC with a low chlorine content (0.41 wt%). It exhibited excellent phenol degradation performance in the Fenton-like system, achieving a degradation efficiency of 95.33% within 30 min under optimal conditions and retaining 91.11% efficiency after five cycles. The performance was significantly superior to that of spherical amorphous carbonbased FeTi/C materials obtained under high chlorine contents (6.7 and 13.78 wt%). Systematic characterization and mechanism investigation revealed that chlorine content could precisely regulate the morphology and graphitization degree of the carbon support. A low chlorine content induced the formation of FeTi/C-350 with a CNT support, which possessed advantages in specific surface area and pore structure. Benefiting from the high electrical conductivity of carbon nanotubes, the Fe2+/Fe3+ redox cycle was accelerated, and center dot OH and center dot O-2(-) were efficiently generated. Phenol mineralization was realized through the heterogeneous synergism among carbon nanotubes, Fe/Ti active sites, and reactive radicals. This study realized the synergy between high-value utilization of PVC solid waste and treatment of phenol-containing wastewater, providing theoretical support for the design of high-efficiency Fenton-like catalysts. The as-prepared FeTi/CNT nanomaterial shows promising application prospects in the treatment of organic pollutants such as phenol-containing coking wastewater.
Supercapacitors (SCs) are promising energy storage devices due to their fast charge-discharge capability, high power density, and excellent cycling stability. Among various electrode materials, Prussian blue (PB) and Prussian Blue Analogues (PBAs) have attracted significant interest because of their open framework, low cost, simple synthesis, and environmentally friendly nature. Their flexible lattice supports rapid ion transport, while multiple transition-metal centers enable synergistic redox activity. PB/PBAs also serve as precursors for derivatives such as metal oxides, sulfides, carbides, and selenides, which offer improved conductivity, more active sites, and enhanced capacitance and stability. Bimetallic and polymetallic derivatives, in particular, show strong potential for high-performance SCs. Despite progress, challenges remain in morphology control, defect reduction, and long-term cycling stability. This review summarizes recent developments in PB/PBA-based electrodes, highlighting synthesis strategies, electrochemical behavior, and structure performance relationships, and outlines future directions for advancing PB-based materials for sustainable energy storage.
Based on the analysis of the conditions necessary for the strict application of the Mott-Schottky method, a methodology for studying thin films based on hydroxyphenyl porphyrins was determined. Sufficiently smooth films of 2H-5,10,15-tri(4-hydroxyphenyl)-20-phenylporphyrin (tris-THPP) and 2H-5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin (tetra-THPP) were obtained by electrochemical deposition initiated by superoxide. The experimental conditions for determining both bulk (type and concentration of the main charge carriers) and surface (flat band potential, density of surface states) characteristics of the semiconductor material are determined. The semiconductor/solution interface impedance was modeled using three different equivalent circuits. It is shown that taking into account adsorption phenomena at the semiconductor/solution interface leads to consistent interpretations of the changes in the calculated characteristics under varying potential. Tris-THPP and tetra-THPP films were found (about 10(25) m(-3)) to have p-type (hole) conductivity. The study showed similar concentrations of charge carriers for tris-THPP and tetra-THPP. The flat band potential under experimental conditions was about +1.52 +/- 0.08 V and 1.16 +/- 0,04 V for tris-THPP and tetra-THPP, respectively. Differences in the surface characteristics of tris-THPP and tetra-THPP materials indicate better prospects for the use of trisTHPP films in photo- and electrocatalytic applications compared to tetra-THPP films.
Titanium dioxide nanotube (TNT) photoanodes were fabricated using a two-step procedure involving the anodization of titanium foil in an ethylene glycol-based electrolyte at 60 V. The resulting TNT/Ti photoanode consists of a layer of anatase-structured polymorphic titanium dioxide nanotubes with an average diameter of 90-100 nm and a wall thickness of 20 nm, the layer thickness being equal to the length of the nanotubes 20-22 mu m. The TNT/Ti photoanode's efficiency in the photoelectrocatalytic oxidation of levofloxacin (LFX) in saline solution was studied. Ultra-performance liquid chromatography coupled with mass spectrometry (UPLC-MS) was used to identify the oxidation products. It was shown that chlorinated LFC, as well as LFC derivatives with dealkylation of the piperazinyl ring, are formed during the initial stage of photoelectrooxidation. Complete transformation of the initial LFX occurs after 50 min of photoelectrolysis at a potential of 0.6 V vs. Ag/AgCl. The quantum efficiency of the photoelectrochemical generation of the active species involved in LFX transformation under 383-nm monochromatic illumination was determined to be 10-12%. A comparison was made between the composition of products formed during photoelectrochemical oxidation of LFX on a TNT/Ti photoanode and its electrocatalytic oxidation on a conventional platinum electrode, as well as energy consumption in both cases.
In anion exchange membrane water electrolysis (AEMWE), the development of anodes that combine high activity with long term durability remains challenging, largely due to the critical role of catalyst layer (CL) and porous transport layer (PTL) integration in controlling interfacial resistance and electronic coupling. To address this issue, a binder free CL and PTL electrode was constructed by in situ hydrothermal growth of NiMoO4 nanowires on Hastelloy fiber papers (HAP). The NiMoO4/HAP anode delivered a current density of 2.072 A cm- 2 at 2.0 V under cathode wet operation at 70 degrees C and sustained 1.697 A cm- 2 under cathode dry conditions. Accelerated stress and durability testing confirmed stable performance over 60 h with only a minor voltage increase. Post test analyses revealed partial molybdenum dissolution accompanied by spontaneous transformation of NiMoO4 into the catalytically active gamma-NiOOH phase. These results demonstrate that substrate engineering, which integrates interfacial coupling with substrate induced doping effects, provides an effective pathway to simultaneously enhance the activity and durability of AEMWE anodes.
Oxide species on Pt electrodes markedly affect the activity of the oxygen reduction reaction (ORR) at the fuel cell cathode. Single-crystal Pd electrodes with a (100) structure exhibit higher ORR activity than their Pt counterparts. However, oxide species on single-crystal Pd electrodes have not been investigated using vibrational spectroscopy in electrochemical environments. Herein, the oxide species on both the low-index planes and n(100)-(111) series of Pd were studied using infrared reflection-absorption spectroscopy (IRAS) and nanoparticle surface-enhanced Raman spectroscopy (NPSERS). A Pd-O-H bending vibration, delta(Pd-O-H) was observed above 0.3 V(RHE) on all surfaces examined. The integrated band intensity followed the order of Pd(100) < Pd(111) < Pd(110). For the n(100)-(111) series, the integrated delta(Pd-O-H) band intensity decreased with increasing (100) terrace width. These tendencies are in complete contrast to those of Pt single-crystal electrodes. The specific ORR activity increased with decreasing delta(Pd-O-H) band intensity, indicating that Pd-OH is an ORR blocking species, as is the case with Pt. NPSERS revealed nu(PdO) and nu(Pd-(OH)) stretching vibrations on the low-index planes of Pd, with band intensities following the same order as that of delta(Pd-O-H) determined using IRAS. However, the nu(PdO) band intensity trend did not correlate with that of the ORR activity, indicating that PdO formation did not govern the ORR activity.
MicroRNA-21 (miRNA-21) is a pivotal tumor marker whose accurate quantification is critical for early disease diagnosis and prognosis. Herein, a highly sensitive and specific electrochemical biosensor was constructed by integrating Cu2+-modified carbon nitride nanocomposites (Cu2+-C3N4) and horseradish peroxidase (HRP) for the quantitative detection of miRNA-21. This strategy harnesses the dual catalytic activity of HRP and Cu2+-C3N4 to mediate the oxidation of 3,3 ',5,5 '-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2), resulting in an enhanced electrochemical current signal. The biosensor exhibited a wide linear detection range of 100 fM to 1 nM for miRNA-21, with a low limit of detection of 71.1 fM. The superior performance of the biosensor is attributed to the synergistic catalytic effect between Cu2+-C3N4 and HRP, combined with the precise molecular recognition of DNA probes. This work provides a novel strategy for the development of low-cost, highperformance biosensors for the detection of tumor-related miRNAs, holding potential for clinical bioanalysis and disease diagnosis.
Pt-based catalysts still face critical challenges in ethanol electrooxidation, including severe poisoning by reaction intermediates and a strong tendency toward the low-efficiency 2-electron acetaldehyde pathway, resulting in insufficient activity and poor stability. Herein, CeO2(x) with tunable oxygen vacancy (VO) concentrations were synthesized by adjusting Ar plasma etching time (x = 0, 15, 30, 45, 60 min). Pt-CeO2(x)/GN catalysts were prepared via ultrasonic self-assembly between Pt/GN and CeO2(x) in ethylene glycol. During this process, Pt nanoparticles migrated from GN onto CeO2 nanorods, forming a compact three-phase interface, while the reducing environment further enriched VO. Among all samples, the optimized Pt-CeO2(30)/GN catalyst delivered the highest electrocatalytic activity toward ethanol oxidation, 2.90 and 2.22 times that of Pt/GN and Pt-CeO2(0)/ GN, respectively. It also exhibited outstanding cycling stability, with 73.35% of the maximum current density retained after 1000 cycles. The enhanced performance arises from three synergies: remarkably reduced charge-transfer resistance at the VO-rich interface (18.95% VO); accelerated hydroxyl generation on CeO2(30) for oxidative removal of toxic intermediates on Pt; and a downshifted d-band center of Pt that weakens intermediate adsorption. Benefiting from this strong interfacial interaction, ethanol can be efficiently oxidized via the 4-electron pathway and the 12-electron pathway involving C-C bond cleavage.
Carbon-based transition-metal electrocatalysts with one-dimensional porous nanofibrous architectures generally exhibit favorable electrical conductivity and abundant exposed defects, making them attractive for bifunctional electrocatalysis. However, densely stacked fibrous networks often suffer from sluggish electrolyte infiltration and inefficient gas escape, while transition-metal species are also prone to aggregation during high-temperature treatment, resulting in insufficient active-site utilization and restricted catalytic performance. In this work, a morphology-reconstruction strategy is developed to fabricate hierarchically porous FeCo-carbon microspheres for efficient bifunctional electrocatalysis in alkaline media. A formamide-assisted FeCo coordination precursor, together with a PTFE-containing electrohydrodynamic system, which induces jet breakup via Rayleigh instability and enables an in situ transition from conventional continuous fibers to three-dimensional porous microspheres. The obtained FA-FeCo@PMS catalyst consists of highly dispersed FeCo species embedded within a defect-rich N/ O/P-doped porous carbon framework. Benefiting from the reconstructed porous microsphere architecture and the homogeneous distribution of active species, FA-FeCo@PMS exhibits enhanced electrolyte accessibility, facilitated gas diffusion, and improved interfacial charge-transfer behavior. Electrochemical measurements in 1.0 M KOH demonstrate that FA-FeCo@PMS delivers overpotentials of 300 and 350 mV at 10 and 50 mA cm-2 for the oxygen evolution reaction, respectively, together with an HER overpotential of 175 mV at 10 mA cm-2, as well as satisfactory long-term durability and low charge transfer resistance. This work provides a feasible strategy for simultaneously regulating catalyst morphology and active-species dispersion toward efficient bifunctional electrocatalysis.
The design and optimisation of catalysts are pivotal to enhancing the efficiency of water electrolysis. Controlling catalyst morphology has emerged as a core strategy for improving hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performance by increasing the exposure of active sites, optimising charge transport pathways, and regulating the adsorption energy of reaction intermediates. However, current research lacks a systematic review and in-depth discussion of the relationship between different dimensional morphologies and their performance enhancement mechanisms. This paper provides a systematic review of research progress in morphology-controlled synthesis methods, including electrospinning, hydrothermal/solvothermal synthesis, chemical vapour deposition and electrodeposition. It establishes an analytical framework centred on active sites, adsorption free energy and charge transport, systematically summarises the structural characteristics of typical 0D/1D/2D/3D morphologies and the pathways through which they enhance performance, and further distils the design principles and underlying mechanisms governing these morphologies. Based on the above analysis, we have systematically summarised the application scenarios and design principles for different morphological dimensions, providing a reference framework for selecting catalysts tailored to specific requirements. Finally, we outline future directions, including the collaborative design of multi-scale morphologies, the precise regulation of active sites at the atomic level, and the shift from empirical trial and error to rational design, with the aim of providing theoretical guidance and design concepts for the research into highly efficient, stable and low-cost water electrolysis catalysts.
Understanding how illumination intensity selects surface reaction pathways is central to designing efficient photoelectrochemical (PEC) water-oxidation systems. Here we combine variable-intensity illumination (0.25 to 6.21 Suns) with photoelectrochemical impedance spectroscopy (PEIS) on thin (similar to 50 nm) ALD-grown alpha-Fe2O3 photoanodes in 1 M KOH to interrogate surface-state kinetics during oxygen evolution. The water-oxidation rate constant k(wo), extracted from steady-state photocurrent and integrated surface-state capacitance, scales with surface hole density rather than total photocurrent, consistent with Helmholtz-layer charging driving interfacial kinetics. The surface hole density saturates beyond similar to 2 to 3 Suns while photocurrent rises near-linearly, a decoupling that a single-state OER model cannot reconcile. A ferrocyanide hole-scavenger control resolves this: decomposing photocurrent shows that surface injection efficiency (eta(injection), 29 to 68%), not bulk separation (eta(separation), 10-14%), governs the photocurrent, accounting for 67% of the per-Sun-normalized rise, while eta(injection) converges to unity above 1.4 V-RHE. A pseudo-first-order analysis of ln k(wo) versus h(s)(+) and a non-monotonic apparent Tafel slope (134-171 mV dec(-1)) reveal a kinetic transition at high flux that single-channel kinetics forbid. Ultrathin Ga2O3 overlayers act as a selective, non-catalytic surface-state modifier: thin layers preferentially suppress mid-gap states that store holes without contributing to photocurrent while leaving productive Fe-oxo pathways intact, whereas thick (9-cycle) overlayers initially suppress all surface charge accumulation and then recover through partial etching of the excess overlayer under OER, suggested by chronoamperometry and fast cyclic voltammetry. Together these results provide impedance-based evidence for two kinetically distinct surface channels on hematite during OER, a productive Fe-oxo route and a secondary peroxo-type state that acts mainly as a recombination center at low illumination but contributes to a parallel cooperative pathway under high hole density.
