Rotating Disk Electrode Measurements Research Articles

Study of Oxygen Reduction Reaction on Polycrystalline Rhodium in Acidic and Alkaline Media

This study examines the kinetics and mechanism of the oxygen reduction reaction (ORR) on a polycrystalline rhodium electrode (Rh(poly)) in acidic and alkaline media, using rotating disc electrode measurements. This study found that the ORR activity of the Rh(poly) electrode decreases in the order of 0.1 M NaOH > 0.1 M HClO4 > 0.05 M H2SO4 concerning the half-wave potentials. The Tafel slopes for ORR on Rh(poly) in the cathodic direction are 60 and 120 mV dec−1 at low and high overpotentials, respectively, in perchloric acid and alkaline solutions. However, strongly adsorbed sulfate anions hinder the ORR on Rh(poly) in sulfuric acid, leading to higher Tafel slopes. The highest ORR activity of Rh(poly) in an alkaline media suggests the promoting role of the specifically adsorbed OH− anions and RhOH. In all cases, ORR on Rh(poly) proceeds through the 4e-series reaction pathway.

Efficient photocatalytic molecular oxygen activation by TTF-based heterojunction for water purification

Tetrathiafulvalene (TTF), one of the well-known organic photoelectric materials, was served as active sites to accelerate the activation of molecular oxygen to degrade organic pollutants. Herein, a kind of Z-scheme heterojunction photocatalysis was constructed based on g-C3N4 and TTF. According to the experimental results, the mechanism of Z-scheme heterojunction was supported, in which photogenerated electrons transferred from g-C3N4 to TTF. More importantly, TTF on the catalyst surface could serve not only as electron donor, but also as the terminal active site to transfer photoexcited electrons to adsorbed oxygen molecules, producing mass of ⋅O2–. Meanwhile, the activation rate constant of TCN-5 for RhB was 0.0624 min−1, which was 10 and 5 times of g-C3N4 and TTF, respectively. In addition, the results of EPR spectra, rotating disk electrode measurement and molecular oxygen activation measurement also demonstrated that this catalyst was energetically favorable to generate ⋅O2– through the single-electron reduction pathway of molecular oxygen. Finally, four possible photodegradation routes for RhB were proposed based on the results of HPLC-MS. This work provides a new insight on the application of organic photoelectric materials in the purification of wastewater by the molecular oxygen activation.

Iron Triad-Based Bimetallic M–N–C Nanomaterials as Highly Active Bifunctional Oxygen Electrocatalysts

Iron Triad-Based Bimetallic M–N–C Nanomaterials as Highly Active Bifunctional Oxygen Electrocatalysts

Catalyst Interaction in Unitized Regenerative Fuel Cells

Unitized regenerative fuel cells have emerged as promising energy conversion and storage systems for various applications. However, in order to optimize their efficiency, it is crucial to enhance the performance of the bifunctional catalyst. This study aims to provide deeper insights into the electrochemical behavior and performance of the bifunctional catalyst. Several electrocatalysts were prepared and evaluated using rotating disc electrode measurements. The primary focus was placed on investigating the interaction between Pt, Ir, and the support material, antimony doped tin oxide (ATO), and their impact on the oxygen evolution reaction and oxygen reduction reaction. Among the analyzed catalysts, Pt black mixed with synthesized IrO2 supported on developed ATO exhibited the highest performance, considering the results from both the fuel cell and electrolyzer systems.

Investigating the Applicability of Rotating Disk Electrode Measurements for Determining Catalyst Activity in Fuel Cells

Currently, the mass production of fuel cells is mainly limited by the availability and the price of platinum, which is typically used as the catalyst for the hydrogen oxidation reaction (HOR) as well as for the oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFC). To eliminate or at least reduce this limitation, it is necessary to develop new catalytic systems, which are based on other, cheaper active components or at least require less platinum. For the characterisation of catalysts, many different methods are in use for the physical and the chemical part. For example, the rotating disk electrode (RDE) is a widely used method for characterizing catalysts in electrochemistry. However, RDE measurement does not reflect the same reaction conditions as exist in a fuel cell. Nevertheless, characterisation by RDE tests is often used for pre-selection at an early stage of catalyst development. In later stages of development, catalyst investigations are carried out by full-cell or half-cell tests.In this work, we will compare the oxygen reduction reaction (ORR) properties of Pt/C catalysts from RDE measurements with those from CCM measurements in half-cell and full-cell configurations to determine what correlations can be made between the different type of investigations.

Towards Low Iridium Loading in Proton-Exchange Membrane Water Electrolysis: Scalable Synthesis of IrOx@TiO2 Core-Shell Particles

Proton-exchange membrane water electrolysis (PEMWE) is a promising technology for producing hydrogen from renewable energy sources. However, the high demand for noble metals hinders the widespread adoption of this technology. Especially the anodic catalyst layer is usually manufactured with high loadings of the scarce element iridium, typically ~2 mgIr·cm-2. As an active and stable noble-metal-free alternative to iridium catalysts has yet to be developed, the most viable strategy for the near future development of PEMWE is to reduce iridium loadings as much as possible. Lowering the iridium loading to values below 0.5 mgIr·cm-2, however, often leads to inhomogeneous catalyst layers resulting in disconnected catalyst islands.1, 2 In two related contributions, we report a novel anodic catalyst for PEMWE that can overcome this limitation by forming homogeneous layers even at lower loadings, thus exhibiting high full cell performance. In this first contribution, we synthesized catalysts with less than 50 wt% iridium content to obtain low iridium loadings while maintaining electrical conductivity. The catalyst is based on the IrO2@TiO2 core-shell microparticles introduced in our previous work,3 which we optimized towards their structural and electrochemical properties. The structural properties of these novel catalysts are analyzed by scanning transmission electron microscopy (STEM), X-ray photoelectron spectroscopy (XPS), and X-ray diffraction (XRD). Furthermore, the catalytic activity is evaluated by rotating disk electrode (RDE) measurements, and the electrochemical stability is assessed in a scanning flow cell setup combined with an inductively coupled plasma mass spectrometer (SFC-ICP-MS). Our catalysts outperform state-of-the-art materials in terms of mass activity in RDE measurements, while a comparable dissolution stability is achieved, as evidenced by SFC-ICP-MS measurements. In our second contribution, we show a high performance of this novel catalyst in catalyst-coated membrane (CCM) configuration with iridium loadings below the above mentioned threshold of 0.5 mgIr·cm-2. This proves that our novel IrOx@TiO2 particles with low iridium contents enable a significant reduction of iridium for the anode in PEMWE.

Benchmarking Activity and Stability of Layered Double Hydroxides (LDHs) Electrocatalysts for Alkaline Water Electrolysis

In order to reduce the cost of producing hydrogen through water electrolysis, novel technologies must be improved. Recently, the merging of conventional alkaline electrolysis (AEL) and proton exchange membrane electrolysis (PEM) has led to the development of anion exchange membrane electrolysis (AEMWE), which offers several advantages over AEL and PEM. In a nutshell, this technique employs cheap, abundant, and easily available (non-geostrategic) transition metals with anionic exchange membranes, overcoming the drawbacks of AEL and PEM.[1]To reach the readiness level of this technology, new and scalable synthetic routes for catalysts that lower the overpotential of the sluggish oxygen evolution reaction (OER) are required. Amongst all the OER catalysts reported in the literature, Layered Double Hydroxides (LDHs) have gained increasing attention due to their low overpotentials and stabilities.[2] Besides, electrochemical protocols to determine the activity and stability of these catalysts in different electrochemical cells must be established to understand their properties. Thus, this work focuses on the advantages and limitations of different electrochemical techniques, such as rotating disk electrode (RDE), three-electrode cells, and single-cell tests, to determine the activity and stability of two different LDHs. Unlike laboratory scale LDHs ‒prepared by hydrothermal treatment (HT-LDH)‒ room temperature synthesized LDHs (RT-LDH) can be prepared in kilogram quantities and present chemical structure and morphology differences. In this work, the LDHs have been characterized with spectroscopic techniques to correlate the chemical structure and morphology of the materials to their electrochemical response by RDE, three-electrode cells, and single-cell measurements.All in all, the scalable RT-LDH presents higher activity compared to HT-LDH in all three techniques. On the one hand, small current densities can only be reached by RDE, and the short-term stability of the materials is affected by the catalyst layer interface. On the other side, single-cell test measurements require long operational times, and the contribution of the membrane degradation to the overall cell voltage is still unclear. Thus, three-electrode cell measurements offer the possibility of characterizing LDHs at relevant current densities in a fast and straightforward manner, without membrane contributions, and are further employed in this work to study the stability of these systems.

Development of Highly Active Pt/C-Based Catalysts for the ORR Using an Ordered Mesoporous Carbon with Network Structure As a Support Material: Focus on the Pt Loading Process

[Introduction]In order to improve the performance of polymer electrolyte fuel cells (PEFCs) for automobiles, ordered mesoporous carbons (OMCs) have attracted attention as supports for Pt as a cathode catalyst. Our research team has successfully synthesized a network-structured OMC (Net-OMC), in which primary OMC particles on the order of several tens of nanometers have a strong network structure, unlike conventional OMC particles, which are typically several micrometers in size. The Net-OMC consists of nanometer-order primary particles, and well-developed macropores (primary and secondary pores) derived from the network structure, which realizes both high Pt dispersion and efficient mass transport. In addition, Pt nanoparticles supported on Net-OMC should be loaded within the nanopores at an appropriate depth position. This will allow the nanopores to be accessible while preventing direct contact between the Pt surface and the ionomeric binder, with resulting poisoning, while also maintaining effective proton transport.RDE measurements revealed that the Pt/Net-OMC catalyst showed higher mass activity for the ORR and higher durability for potential-step cycling compared with a commercial Pt/CB catalyst [1]. These results suggest that the aggregation and sintering of the Pt particles were successfully suppressed due to the nanopore structure.In order to further improve the catalytic activity of the Pt/Net-OMC catalyst, it is also necessary to uniformly load Pt into the nanopores at an appropriate size and depth during catalyst preparation. However, even when using the colloidal technique, which has been established for loading Pt on carbon black, it has been difficult to achieve good Pt dispersibility with conventional protocols due to the tendency of the Pt to aggregate on the Net-OMC [2]. Therefore, in this study, the conventional colloidal technique was optimized for loading Pt on the Net-OMC support.[Experimental]Loading of PtOx on Net-OMC was carried out by mixing an aqueous solution of PtOx colloid with an aqueous dispersion of Net-OMC powder, followed by heat treatment at an appropriate temperature. During this process, the slurry pH (pH 3~11), heating temperature (40~80 °C) and heating time (10~180 min) were varied to investigate their effects. The resulting slurries were then filtered, dried and reduced at 300 °C for 3 hours in flowing hydrogen to obtain Pt/Net-OMC.The morphology of the Pt/Net-OMC was observed by transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). Cyclic voltammetry and linear sweep voltammetry were carried out using the conventional rotating disk electrode (RDE) technique. Furthermore, membrane-electrode assemblies (MEAs) were prepared using Pt/Net-OMC as a cathode catalyst and evaluated for catalytic activity according to an FCCJ protocol using a Japan Automobile Research (JARI) standard cell.[Results and Discussion]The variation of Pt loading behavior with slurry pH revealed that Pt tended to aggregate when the pH was below 5, while the Pt loading amount significantly decreased when the pH was above 6 (Fig. 1, Table 1). These results indicate that the optimum slurry pH was ca. 5.5 to obtain a high dispersion of Pt. It was also found that the optimum temperature for Pt loading was ca. 50 °C; when the temperature was below 40 °C, the loading amount decreased significantly, and when the temperature was above 80 °C, some of the Pt particles formed aggregates. It was also found that the Pt particles showed continuous growth, with a linear dependence of the Pt aggregate size on the loading time at 50 °C.Based on the TEM observation, the average Pt particle size on the Pt/Net-OMC that had been heated at 50 °C for 1 hour was ca. 3 nm, and the particles exhibited good dispersion. Also, the correlation between the supported state of Pt and the catalytic activity of the Pt/Net-OMC will be discussed in detail.[1] T. Miyao, H. Nishino, H. Yamazaki, S. Sato, K. Tamoto, M. Uchida, A. Iiyama, K. Shibanuma, N. Koizumi, , the 242nd ECS Meeting, #I01D-1578.[2] M. Watanabe, M. Uchida and S. Motoo, J. Electroanal. Chem., 229, 395-406 (1987)Acknowledgement: This work was partially supported by the ECCEED’30-FC project from NEDO. Figure 1

ORR Activity and Voltage-Cycling Stability of a Carbon-Supported PtxY Alloy Catalyst Evaluated in a PEM Fuel Cell

Platinum-yttrium alloys (PtxY) are suggested to have superior oxygen reduction reaction (ORR) activity and long-term stability in proton exchange membrane fuel cells (PEMFCs). However, the actual ORR activity and stability of a PtxY catalyst with a high electrochemically active surface area (ECSA) in a PEMFC remains uncertain. Here, a Ketjen black (KB) carbon supported PtxY/KB catalyst with a high ECSA (∼60 m2/g) was synthesized using a carbon nitride precursor. Based on elemental analysis, XRD, electron microscopy, and a mass-balance based model, it was shown that the acid-leached PtxY nanoparticles of the catalyst consist of a ∼0.7 nm thick Pt-shell and a Pt3Y core. Rotating disk electrode (RDE) and 5 cm2 single-cell PEMFC measurements indicated that the ORR activity of the acid-leached PtxY/KB catalyst is similar to an analogously synthesized Pt/KB reference catalyst with the same ECSA. Voltage-cycling accelerated stress tests (ASTs) between 0.6−1.0 V (in H2/N2 at 80 °C/95% RH) in 5 cm2 single-cells showed that the ORR activity and durability of the PtxY/KB catalyst is similar to that of the Pt/KB reference catalyst. Thus, the high durability of Pt-rare Earth alloys that has been claimed on the basis of RDE measurements is not observed in actual PEMFCs.

Interaction of Catalysts for Unitized Regenerative Fuel Cells

Unitized regenerative fuel cells have emerged as promising energy conversion and storage systems for various applications. However, in order to optimize their efficiency, it is crucial to enhance the performance of the bifunctional catalyst. This study aims to provide deeper insights into the electrochemical behavior and performance of the bifunctional catalyst. Several electrocatalysts were prepared and evaluated using rotating disk electrode measurements. The focus was placed on investigating the interaction between Pt, Ir, and the support material, antimony doped tin oxide (ATO), and their impact on the oxygen evolution reaction and oxygen reduction reaction. Among the analyzed catalysts, Pt-black mixed with synthesized IrO2 supported on developed ATO exhibited the highest performance, considering the results from both the fuel cell and electrolyzer systems.

Effects of Bifunctional Oxygen Catalyst Layer Composition on Unitized Regenerative Fuel Cell Performance

Proton exchange membrane unitized regenerative fuel cells (PEM-URFCs) can generate storable fuel (hydrogen) and oxidant (oxygen) which can then be used to produce power from the same cell. Combining electrolysis and fuel cell modes within the same cell allows PEM-URFCs to have the potential for lower mass, volume, and cost compared with discrete fuel cell and electrolyzer systems. The bifunctional oxygen catalyst layer (BOCL) catalyzes the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR) at the same electrode, and there are wide potential differences and opposing mass transport phenomena involved within the BOCL when operating in electrolyzer or fuel cell mode. The BOCL composition, structure and morphology significantly affect performance and stability of PEM-URFCs. In our prior work, we showed bimetallic nanoframes provide bifunctional oxygen electrocatalysts with significantly higher activity compared with monometallic structures, evaluated using a rotating disk electrode configuration.1 We will present our investigation of the effects of the BOCL composition, structure and morphology on URFC membrane electrode assemblies (MEAs) prepared using ultrasonic spraying. Catalyst composition and loading were determined to influence URFC performance, and there are tradeoffs between fuel cell performance, electrolyzer performance, and catalyst cost. In addition to the effects of the active catalyst (either Pt for ORR or IrO2 for OER), our work supports the non-catalytically active component influences MEA performance, which is in agreement with our finding of synergistic effects of Pt and IrO2 within rotating disk electrode measurements.1 We are also evaluating the effects of porous transport layers and different operating conditions on URFC MEA performance and durability over repeated cycling. References Godínez-Salomón, F.; Albiter, L.; Mendoza-Cruz, R.; Rhodes, C.P. Bimetallic Two-dimensional Nanoframes: High Activity Acidic Bifunctional Oxygen Reduction and Evolution Electrocatalysts. ACS Appl. Energy Mater. 2020, 3, 2404-2421.

Composition-Dependent Electrocatalytic Behavior in First-Transition Metal Nanowires Toward the Oxidation of Small Organic Molecules

Platinum-based catalysts are widely used for the electrochemical oxidation of small organic molecules (SOMs), including methanol, ethanol, and glucose. However, it has some limitations, including high cost and limited availability. Platinum’s performance is also hindered by the formation of carbon monoxide (CO) and other partially oxidized intermediates that strongly bind to the surface and hinder kinetics at low overpotentials. Binary alloys created from Pt and other more abundant transition metals aim to reduce the cost of Pt catalysts as well as alleviate the effects of the CO intermediate on Pt catalysts, thus enhancing the catalytic performance of pure Pt. In this project, we synthesize, characterize, and evaluate the electrocatalytic performance of one-dimensional electrocatalysts created from transition metal nanowires coated with precious metal catalysts. These core-shell NWs were synthesized using a template-based technique that allows for the creation of nanowires of different sizes and compositions. The nanowires were characterized using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and powder X-ray diffraction (XRD). The catalytic performance of these NWs toward SOM oxidation was evaluated in acidic conditions utilizing cyclic voltammetry and linear sweep voltammetry. We also investigate the performance of these catalysts toward the oxygen reduction reaction (ORR) utilizing rotating disk electrode measurements. The results reveal that the characteristics of the catalytic performance of the alloy NWs are dependent on their morphology and composition.

Electrochemical formation of Sn films on copper by overpotential and underpotential electrodeposition in deep eutectic solvents

The electrodeposition process of tin films on copper electrodes in ethaline and reline deep eutectic solvents (DES) was studied in the 303 – 353 K range. Voltammetric data indicate the presence of underpotential and overpotential electrodeposition processes. While the former occurs under surface-reaction control, the latter proceeds under mass transport control. Electrochemical impedance spectroscopy shows two capacitive contributions during the underpotential process and a single capacitive contribution at high frequencies and a Warburg contribution at low frequencies, when the electrodeposition process takes place in the overpotential region. Tin deposits obtained in ethaline exhibit blunt particles with ordered structures whereas in reline facetted particles with no preferential order are observed as electrodeposition time is increased. The electrocrystallization mechanism under overpotential conditions in ethaline and reline corresponds to an instantaneous nucleation and a 3D growth process. For underpotential conditions in ethaline, an instantaneous nucleation and 2D growth coupled to an adsorption process occurs. XRD spectra shows the formation of Cu3Sn and Cu6Sn5 intermetallics due to the diffusion of Sn atoms into the Cu lattice during the electrodeposition process. From rotating disk electrode measurements, the diffusion coefficient of Sn(II) ions in both DES at different temperatures, and the diffusion activation energy, were determined.

Valorization of Naturally Abundant Low-Value Peat into Highly Active Non-Platinum Group Metal Oxygen Reduction Catalysts

This work explores the feasibility of synthesizing active non-platinum group metal oxygen reduction catalysts from naturally abundant peat through a facile one-pot method. The procedure yielded highly porous materials (specific surface area ~1000 m2 g-1) with promising oxygen reduction activity. Onset and half-wave potential values of 0.93 and 0.83 V vs RHE, respectively, were attained in rotating disc electrode experiments for the most active catalyst synthesized using dicyandiamide. Notably, the choice of nitrogen precursor influenced both the porosity and the electrochemical activity. Finally, the best-performing catalyst was analyzed in a rotating ring disc electrode setup, where the results confirmed those obtained in rotating disc electrode measurements.

Zinc porphyrin/g-C3N4 S-scheme photocatalyst for efficient H2O2 production

Constructing heterojunction photocatalyst is a promising strategy to achieve solar-to-chemical energy conversion. Especially, the S-scheme heterojunction has received a great deal of attention because of its superiority of the efficient photogenerated charge carriers’ separation and the strong photoredox capacity. Herein, an S-scheme heterojunction is designed and synthesized through grafting supramolecular Zinc porphyrin (Zn-TCPP) on g-C3N4 (CN) via –CONH- bridging bond for H2O2 production in the O2 atmosphere under a 300 W Xe lamp irradiation using ethanol as a sacrificial agent. As the optimal sample, Zn-TCPP/CN exhibits the highest H2O2 production rate with 532.7 μmol/L within 90 min, which is 3.1 and 9.0 times higher than those of pure CN and Zn-TCPP, respectively. The route of H2O2 production in the photocatalytic process and the mechanism of activity enhancement are revealed by a systematic characterisation. Hence, the results of the radical trapping experiment and rotating disk electrode measurement demonstrate that the two-step single-electron route is the predominant reaction step in the process of H2O2 generation. In-situ irradiated X-ray photoelectron spectroscopy (ISI-XPS) and Kelvin probe force microscopy (KPFM) technology provide strong evidence of the S-scheme charge transfer path between Zn-TCPP and CN, which greatly facilitates the spatial charge separation. Meanwhile, the density functional theory (DFT) calculations reveal that the strong interface interaction between Zn-TCPP and CN can induce the electron delocalization effect, thus restraining charge recombination. This work inspired the design of a high-active metalloporphyrin-based S-scheme heterojunction for energy conversion.

Electrochemistry and Stability of 1,1'-Ferrocene-Bisphosphonates.

Here, we investigate the electrochemical properties and stability of 1,1'-ferrocene-bisphosphonates in aqueous solutions. 31P NMR spectroscopy enables to track decomposition at extreme pH conditions revealing partial disintegration of the ferrocene core in air and under an argon atmosphere. ESI-MS indicates the decomposition pathways to be different in aqueous H3PO4, phosphate buffer, or NaOH solutions. Cyclovoltammetry exhibits completely reversible redox chemistry of the evaluated bisphosphonates, sodium 1,1'-ferrocene-bis(phosphonate) (3) and sodium 1,1'-ferrocene-bis(methylphosphonate) (8), from pH 1.2 to pH 13. Both the compounds feature freely diffusing species as determined using the Randles-Sevcik analysis. The activation barriers determined by rotating disk electrode measurements revealed asymmetry for oxidation and reduction. The compounds are tested in a hybrid flow battery using anthraquinone-2-sulfonate as the counterside, yielding only moderate performance.

Rotating disk electrode measurements on low and high loading catalyst layers: Diffusion limitations and application to Pt catalysts supported on porous micrometric carbon xerogel particles designed for proton exchange membrane fuel cells

Innovative fuel cell catalysts are now often being supported on nanostructured materials in order to improve mass transport, contact with the ionomer and active phase distribution. However, to maintain their inner structure, these supports are used as µm-sized particles, which hampers to perform accurate kinetic experiments on rotating disk electrode since a thin layer of catalyst is in principle required. The present study thus aims at checking if accurate measurements remain possible for thick layers of large particles. To do so, oxygen reduction was first performed on a commercial Pt catalyst supported on carbon black; both a typical thin and a thick layer (37 and 370 µgPt cm−2) were used. The impact of the diffusion limitations on the kinetic current was determined. The same measurement protocol was then performed with a catalyst supported on 5 µm particles of a nanostructured carbon (∼15 µm layer thickness, 370 µgPt cm−2). Results and calculation show that, for both thick layers, the kinetic current should be measured at higher potential (1.00 or 1.05 V/ESH) than usual to avoid diffusion limitations. Also, the voltage scanning rate should be lowered to 0.5 or 1 mV s−1 to decrease the impact of the double layer capacity on the measurements.

Schottky barrier height mediated Ti3C2 MXene based heterostructure for rapid photocatalytic water disinfection: Antibacterial efficiency and reaction mechanism

Schottky barrier plays a key role in determining the interface electron transfer of most Schottky junctions, but the relationship between schottky barrier height (SBH) and photocatalytic disinfection activity is not clearly revealed. Here, a well-designed tubular graphitic carbon nitride/hydroxyl terminated Ti3C2 MXene (TCN/TC(OH)) Schottky junction with controllable SBH was prepared as a model case for investigation. Experimental study and density functional theory calculation confirm that the surface hydroxyl termination of Ti3C2 can lower the SBH of TCN/TC(OH) by reducing its work function (0.23 eV). The lowered SBH ensures rapid interface transfer of photogenerated electron, which decreases the average surface recombination rate from 0.0077 s−1 (TCN/TC) to 0.0045 s−1 (TCN/TC(OH)-3) and increases the corresponding surface charge transfer efficiency from 48.2% to 53.2%. Rotating disk electrode measurement confirms that different from the two-step single-electron O2 reduction of TCN/TC (n = 1.54), TCN/TC(OH)-3 (n = 1.95) exhibits a one-step two-electron reduction route, which is more selective for the generation of the major antibacterial reactive oxygen species H2O2. Consequently, TCN/TC(OH)-3 presents much higher photocatalytic performance towards natural water disinfection, and can entirely inactivate 7 × 107 CFU/mL of Staphylococcus aureus even in complex water matrix (interfering ions, acidic solution and real water samples). Our work provides a feasible guidance for future natural water purification by interfacial engineering of the MXene-based Schottky junction.

Modeling Anion Poisoning during Oxygen Reduction on Pt Near-Surface Alloys

Electrolyte effects play an important role in the activity of the oxygen reduction reaction (ORR) of Pt-based electrodes. Herein, we combine a computational model and rotating disk electrode measurements to investigate the effects from phosphate anion poisoning for the ORR on well-defined extended Pt surfaces. We construct a model including the poisoning effect from phosphate species on Pt(111) and Cu/Pt(111) based on density functional theory simulations. By varying the subsurface Cu content of the Cu/Pt(111) alloy, we tune the *OH binding energies on the surface by means of ligand effects, and as a result, we tune the ORR activity. We have investigated the effect of adsorbed phosphate species at low overpotentials when tuning *OH binding energies. Our results display a direct scaling relationship between adsorbed *OH and phosphate species. From the model, we observe how the three-fold binding sites of phosphate anions limit the packing of poisoning phosphate on the surface, thus allowing for *OH adsorption even when poisoned. Our work shows that, regardless of surface site blockage from phosphate, the trend in the catalytic oxygen reduction activity is predominantly governed by the *OH binding.

How Effective Is Graphitization of Biomasses for the Carbon Stability of Pt/C ORR Catalysts?

Catalysts for the oxygen reduction reaction (ORR) in PEM fuel cells are commonly constituted of Pt-based nanoparticles and a carbon support originating from fossil resources. In order to employ a more sustainable carbon support, activated sawdust was chosen in this study. This was firstly steam-activated at 750 °C and then thermally treated at elevated temperatures up to 2800 °C and reducing conditions at 1100 °C. Various physical characterization methods were applied to systematically relate treatment parameters to surface and structural properties of the carbon material. Deposition of small Pt nanoparticles on the biochar-based supports yielded in ORR active catalysts which were analyzed by thin-film rotating disc electrode measurements. The activity and stability towards the ORR of these novel catalysts was compared to a commercial raw oil-based Pt/C and the influence of support modification on the ORR performance was discussed.