CO Stripping Voltammetry Research Articles

Quantitative Differential Electrochemical Mass Spectroscopy Analysis of Electrochemical Carbon Corrosion Reactions in Alkaline Electrolyte Solutions

Introduction Zinc-air secondary batteries are attracting attention as next-generation large-scale energy storage devices. However, one of the challenges for practical application is the prevention of air electrode degradation caused by the oxidative corrosion of carbon. In order to suppress the carbon corrosion reaction, clarification of the reaction mechanism is required. The differential electrochemical mass spectrometry (DEMS) is the in-situ mass spectrometry for the volatile species generated by electrochemical reactions, and it is possible to measure the partial current of the carbon corrosion reaction by analyzing CO2 evolution. Therefore, DEMS has intensively been applied to carbon corrosion reactions under acidic conditions. However, applying DEMS to alkaline electrolyte systems is challenging due to the relatively high solubility of CO2 as carbonate ions. On the other hand, we have constructed a new DEMS measurement system combining a microreactor and an ion-exchange membrane and quantitatively analyzed CO2 evolution in an alkaline aqueous solution [1]. However, the current measurement system had relatively low temporal resolution and large IR-drop. In this study, we constructed the DEMS measurement system with improved temporal resolution and reduced IR-drop. Experimental A schematicof the electrochemical three-electrode cell used for the DEMS measurement is shown in Fig.1.A platinum-supported carbon composite electrode, a Hg/HgO electrode, a Pt wire, and 1 mol dm–3 KOH solution were used as the working, reference, and counter electrodes and the electrolyte solution, respectively. The electrolyte solution was flown into the cell using a syringe pump and acidified with a 1 mol dm–3 sulfuric acid solution in a microreactor installed downstream of the working electrode. The volatile components were installed from the electrolyte solution to the vacuumed chamber through a PTFE membrane interface placed at the downstream of the microreactor. The electrolyte path from the working electrode to the membrane interface was shortened from 13.5 cm to 4.5 cm to improve the temporal resolution of the previous system. In addition, the position of the reference electrode was changed from the outside of the working electrode chamber to inside of that to reduce the IR-drop at the ion-exchange membrane. We also increase the working electrode area from 78.5 mm2 to 201 mm2 in order to enhance the detectivity. CO stripping voltammetry (Eq. (1)) was performed to evaluate the CO2 detection property of the constructed DEMS system.Pt-COad + 2OH– → Pt* + CO2 + H2O + 2e– (1) Results and discussion Fig.1 shows the CO stripping voltammogram and the corresponding mass signal of CO2. CO oxidation current is observed from –0.5 to –0.2 V, while our previous setup showed CO oxidation current from –0.4 to 0.1 V [1]. This result shows that the IR-drop is effectively suppressed in the new DEMS setup. In addition, the mass signal of CO2 is observed in the almost same potential range (–0.5 to –0.1 V) as that of the CO oxidation current, suggesting that the new DEMS setup has improved temporal resolution. On the other hand, the calibration constant (Eq. 2) of new DEMS setup is to the same extent as the previous one [1], indicating that the new DEMS setup has the comparable detectivity. Analyses of catalyst-loading carbon corrosions will also be presented at the site.

Effect of Pt Nanoparticle Morphology on the Aerobic Oxidation of Ethylene Glycol to Glycolic Acid in Water.

Pt nanoparticles (diameter <3 nm), generated by metal vapor synthesis and supported on a high surface area carbon, were used to catalyze the aerobic oxidation of ethylene glycol to glycolic acid (GA) in water under neutral and basic reaction conditions. Controlled heat treatment of the catalyst under a nitrogen atmosphere brought about the formation of a morphologically well-defined catalyst. A combination of atomic resolution electron microscopy, CO stripping voltammetry, and XPS analyses conducted on as-synthesized and heat-treated catalysts demonstrated the crucial role of the nanoparticles' morphology on the stabilization of catalytically highly active Pt-OH surface species, which were key species for the Pt-catalyzed oxidation of the alcohol to the carbonyl functionality. The boosting effect of base on the catalyst' s activity and GA selectivity has been proved experimentally (autoclave experiments). The effect of base on the nonmetal-catalyzed reaction steps (i.e., aerobic oxidation of carbonyl to acid functionality) has been proved by DFT calculations.

Electron gathering at violet phosphorene-Ag interface for photoreduction of CO2 to ethylene

Selective photoreduction of CO2 into ethylene is desirable but stays challenging due to easy desorption of primary reduction product CO. Herein, violet phosphorene nanosheets (VPNS) are for the first time demonstrated to be effective CO2 photoreduction catalysts to yield ethylene. Photoelectron was found to transfer from VPNS to co-catalyst Ag and aggregated on VPNS-Ag interface to enhance CO2 and CO* adsorption, and further lower the reduction energy barrier to yield ethylene, which was confirmed by in-situ diffuse reflectance infrared Fourier-transform, CO stripping voltammetry, CO reduction experiments, and density functional theory calculations. CO2 is reduced into COOH* and automatically transformed into CO* on VPNS-Ag surface, then protonized into CHO* with a low barrier of 0.64 eV and automatically coupled into COCHO* to yield ethylene. Only ethylene was detected from CO2 photoreduction with a yield of 10.34 μmol g−1 h−1 without any hole-sacrificial agent, much higher than most reported photocatalysts.

A hybrid FeOx/CoOx/Pt ternary nanocatalyst for augmented catalysis of formic acid electro-oxidation

Platinum-based catalysts that have long been used as the anodes for the formic acid electro-oxidation (FAO) in the direct formic acid fuel cells (DFAFCs) were susceptible to retrogradation in performance due to CO poisoning that impaired the technology transfer in industry. This work is designed to overcome this challenge by amending the Pt surface sequentially with nanosized cobalt (nano-CoOx, fibril texture of ca. 200 nm in particle size) and iron (nano-FeOx, nanorods of particle size and length of 80 and 253 nm, respectively) oxides. This enriched the Pt surface with oxygenated groups that boosted FAO and mitigated the CO poisoning. The unfilled d-orbitals of the transition metals and their tendency to vary their oxidations states presumed their participation in a faster mechanism of FAO. Engineering the Pt surface in this FeOx/CoOx/Pt hierarchy resulted in a remarkable activity toward FAO, that exceeded four times that of the Pt catalyst with up to ca. 2.5 times improvement in the catalytic tolerance against CO poisoning. This associated a ca. − 32 mV shift in the onset potential of FAO which increased to − 40 mV with a post-activation of the same catalyst at − 0.5 in 0.2 mol L–1 NaOH, displaying the catalyst's competitiveness in reducing overpotentials in DFAFCs. It also exhibited a favorable amelioration in the catalytic durability in long-termed chronoamperometric electrolysis. The electrochemical impedance spectroscopy and the CO stripping voltammetry were employed to elucidate the origin of enhancement.

Cu-Modified Palladium Catalysts: Boosting Formate Electrooxidation via Interfacially OHad-Driven Had Removal.

Direct formate fuel cells have gained traction due to their eco-friendly credentials and inherent safety. However, their potential is hampered by the kinetic challenges of the formate oxidation reaction (FOR) on Pd-based catalysts, chiefly due to the unfavorable adsorption of hydrogen species (Had). These species clog the active sites, hindering efficient catalysis. Here, we introduce a straightforward strategy to remedy this bottleneck by incorporating Pd with Cu to expedite the removal of Pd-Had in alkaline media. Notably, Cu plays a pivotal role in bolstering the concentration of hydroxyl adsorbates (OHad) on the surface of catalyst. These OHad species can react with Had, effectively unblocking the active sites for FOR. The as-synthesized catalyst of PdCu/C exhibits a superior FOR performance, boasting a remarkable mass activity of 3.62 A mg-1. Through CO-stripping voltammetry, we discern that the presence of Cu in Pd markedly speeds up the formation of adsorbed hydroxyl species (OHad) at diminished potentials. This, in turn, aids the oxidative removal of Pd-Had, leveraging a synergistic mechanism during FOR. Density functional theory computations further reveal intensified interactions between adsorbed oxygen species and intermediates, underscoring that the Cu-Pd interface exhibits greater oxyphilicity compared to pristine Pd. In this study, we present both experimental and theoretical corroborations, unequivocally highlighting that the integrated copper species markedly amplify the generation of OHad, ensuring efficient removal of Had. This work paves the way, shedding light on the strategic design of high-performing FOR catalysts.

Enhanced Oxygen Reduction Activity of Platinum Micropore

AbstractThe high overpotential of oxygen reduction reaction (ORR) prevents the wide commercialization of fuel cells and metal‐air batteries. To accelerate the reaction rate, porous electrocatalysts draw attention to obtain a higher specific surface area. However, the effect of micropores on ORR kinetics has not been understood because of the non‐uniform pore sizes, length, and tortuosity of practical electrocatalysts. In this study, we evaluate ORR activity in a micropore using platinum model electrodes with arrays of cylindrical pores with a uniform pore diameter of 1.8 nm. The model electrodes having pore lengths of 45, 100, and 380 nm are fabricated, and their ORR performances are examined by electrochemical measurements and numerical simulations in 0.1 mol dm−3 KOH aqueous solution. The intrinsic ORR activity of the micropore is successfully obtained with the electrode having a pore length of 45 nm, where oxygen transport resistance in the micropore has little effect on ORR. It is found that the intrinsic ORR activity of the micropore is higher than that of a planar Pt surface. X‐ray photoelectron spectroscopy and CO stripping voltammetry indicate a downshift of the d‐band center, which can be the origin of the high intrinsic ORR activity.

Membraneless ethanol fuel cell Pt-Sn-Re nano active catalyst on a mesoporous carbon support.

Herein, we report, for the first-time, mesoporous carbon-supported binary and ternary catalysts with different atomic ratios of Pt/MC (100), Pt-Sn/MC (50 : 50), Pt-Re/MC (50 : 50), Pt-Sn-Re/MC (80 : 10 : 10) and Pt-Sn-Re/MC (80 : 115 : 05) prepared using a co-impregnation reduction method as anode components for membraneless ethanol fuel cells (MLEFLs). Mechanistic and structural insights into binary Pt-Sn/MC, Pt-Re/MC and ternary Pt-Sn-Re/MC catalysts were obtained using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDX) methods. In particular, chemical characterization via cyclic voltammetry, CO stripping voltammetry and chronoamperometry indicated that Pt-Sn-Re/MC (80 : 15 : 05) had better dynamics toward ethanol oxidation than Pt-Sn-Re/MC (80 : 10 : 10), Pt-Sn/MC (50 : 50) and Pt-Re/MC (50 : 50) catalysts. In terms of the single cell performance of the prepared catalysts, Pt-Sn-Re/MC (80 : 15 : 05) (31.5 mW cm-2) showed a higher power density and current density than Pt-Sn-Re/MC(80 : 10 : 10), Pt-Re/MC (50 : 50) and Pt-Sn/MC (50 : 50) at room temperature. The addition of Re into the binary Pt-Sn catalyst improved its electrical performance for ethanol oxidation in a membraneless ethanol fuel cell. As a result, the ternary-based Pt-Sn-Re/MC (80 : 15 : 05) catalyst demonstrated enhanced performance compared to monometallic and bimetallic catalysts in the ethanol oxidation reaction in a membraneless fuel cell.

CO Oxidation Behavior of Pt/RuO2-Sphere Catalyst in Acidic Electrolyte

Polymer electrolyte fuel cells (PEFCs) are one of the candidates for the next-generation power source. PtRu alloy catalyst is used as an anode catalyst because it has high CO poisoning tolerance. It is well known that PtRu alloy has high CO poisoning tolerance because of the bifunctional mechanism and the ligand effects of the Ru atom working as the co-catalyst. However, the Ru atom dissolves during the operation of PEFCs, such as start-up/shut-down, and then the CO poisoning tolerance becomes low. The author reported using ruthenium oxide nanosheet (RuO2ns) acted as high stable co-catalyst [1]. The composition catalyst of traditional Pt/C and RuO2ns (RuO2-Pt/C) showed high CO poisoning tolerance and long life. But the high CO poisoning tolerance site in the RuO2ns-Pt/C catalyst was limited to the very close position of Pt nanoparticles and RuO2ns. Thus, the CO poisoning tolerance was uneven, even within the same catalyst. On the other hand, we reported that new catalyst support with the sphere shape composited by the reduced graphene oxide wall provided high substance diffusion and Pt utilization rate [2]. It is expected that the spherical catalyst support composed from the RuO2ns wall provides complete contact with Pt nanoparticles and not only exquisite CO poisoning tolerance but also high Pt utilization. In this study, the new spherical catalyst support with the RuO2ns wall was synthesized and supported Pt nanoparticles, and its CO oxidation ability was evaluated by CO stripping voltammetry. The spherical catalyst support (RuO2-sphere) was composed of a SiO2 bead as a core and the RuO2ns wall, and its synthesis method was similar to the previous work [2]. Concretely, this study changed the wall material from graphene oxide to RuO2ns. And the Pt complex adsorbing on a RuO2-sphere was reduced by heating reflux with hydrazine at 100°C and 24 hours in ethanol solvent. After water washing, Pt-supported RuO2-sphere (Pt/RuO2-sphere) was obtained. The morphology, crystal structure, and electron state of the Pt/RuO2-sphere were evaluated by SEM, XRD, and XPS, respectively.A three-electrode cell, which is composed of a working electrode, Pt counter, Ag/AgCl reference electrode, and 0.1 M HClO4 electrolyte, was used for the electrochemical measurements, and the measurement temperature was 60°C. This study converted the potentials from Ag/AgCl reference to RHE reference. The CO stripping voltammetry was conducted in the following steps. CO gas was introduced had flowed into the electrolyte for two minutes to adsorb on the metal surface while its potential was kept at 0.05 V. The inert gas purged out excess CO gas in the electrolyte for 30 minutes. And then, the potential was swept to 1.2 V at 10 mV s-1. SEM images of the Pt/RuO2-sphere showed about 500 nm sphere of RuO2-sphere and a few nanometer sizes of Pt particles. Results of XRD and XPS suggested that Pt particles were mainly metallic state and not alloying with Ru. In addition, Ru valence in Pt/RuO2-sphere was predicted at quadrivalent. The cyclic voltammogram of the Pt/RuO2-sphere had characteristic peaks attributed to both Pt and RuO2ns. Specifically, the redox peaks below 0.4 V and at 0.8V-1.2V could be assigned the hydrogen adsorption/desorption and redox of the Pt surface, respectively. In addition, the unique redox peaks of RuO2ns were also observed around 0.6 V. The estimated on-set potential of the CO oxidation peak in the Pt/RuO2-sphere was at 0.36 V, and this value was superior to that of traditional Pt/C and near that of PtRu/C. The CO oxidation peak of the Pt/RuO2-sphere was sharply compared to the composite catalyst of Pt/C and RuO2ns in previous work. This change in peak shape was thought to be attributed to the expansion of the contact sites between the Pt nanoparticles and the RuO2ns surface.Developed Pt/RuO2-sphere catalyst, which had the RuO2ns wall and spherical shape, showed high CO poisoning catalyst as well as PtRu/C.[1] T. Saida, et al., Electrochim. Acta, 55, 857–864 (2010).[2] T. Saida, et al., Energy & Fuels, 36, 1027-1033 (2022).

Quantitative Analysis of CO2 Evolution in an Alkaline Electrolyte Solution By Differential Electrochemical Mass Spectroscopy

CO2 is involved in various main and side reactions of electrochemical energy devices, such as carbon corrosion reactions and alcohol oxidation reactions. Differential electrochemical mass spectroscopy (DEMS) has been intensively applied in acidic electrolyte solutions to analyze these reactions. DEMS is the in-situ electrochemical measurement technique to analyze volatile species with the mass spectrometer (MS). However, the applications of DEMS to alkaline electrolyte solutions have been limited due to the high solubility of CO2 in alkaline solutions. While "conventional DEMS cells," where porous thin-film working electrodes are formed onto polytetrafluoroethylene (PTFE) membrane interface, can quantitatively analyze CO2 that has not dissolved into the electrolyte yet [1], the working electrode materials are limited to those that can be deposited on porous PTFE membrane as porous thin-films. Recently, Möller et al. have developed the DEMS system, which can detect CO2 from general planer electrodes coated by catalyst powders by combining a neutralizer and "dual thin-layer flow cell" [2]. However, due to the relatively low detection limit, quantitative analysis of evolved CO2 has not been accomplished. In this study, we attempt to use high surface area electrodes to enhance the MS signal of CO2 to enable quantitative analysis of evolved CO2. To suppress the in-plane reaction distribution in the flow cell, we integrated an anion exchange membrane into the cell and arranged the counter electrode opposing the working electrode [3] (Fig. 1 (a)).CO-stripping voltammetry was performed to evaluate the CO2 detectability of the constructed DEMS system. The DEMS cell was composed of a commercial Pt/C electrode as the working electrode, a commercial Hg/HgO electrode as the reference electrode, a Pt mesh as the reference electrode, 1 mol dm–3 KOH aq as the electrolyte solution, and 1 mol dm–3 H2SO4 aq as the neutralizer. Figure 1 (b) shows the CO-stripping voltammogram and corresponding MS signal of CO2 (m/z = 44). MS signal of CO2 accompanied by the anodic CO oxidation current is clearly observed from 0.6 to 1.2 V vs. RHE. The calibration constant, which correlates the MS signal of CO2 to partial current for CO2 evolution reaction, is successfully obtained as 2.2 × 10–10, which shows that the DEMS system established in this study can quantitatively analyze CO2. Applications to the carbon corrosion reactions are also presented at the site.

Quantitative DEMS analysis of CO2 evolution reactions in alkaline electrolyte solutions

CO2 evolution is involved in various main and side reactions of electrochemical systems, such as carbon corrosion reactions and alcohol oxidation reactions. Differential electrochemical mass spectroscopy (DEMS) has been intensively applied to analyze the partial current of the CO2 evolution reaction in acidic and neutral electrolyte solutions. However, the quantitative analysis of the CO2 evolution reaction in alkaline electrolyte solutions has not been successful when catalyst-loaded carbon electrodes were applied, due to the high solubility of CO2 in the electrolyte. In this study, we develop a new DEMS system combining microreactor and ion exchange membrane to quantitatively analyze CO2 evolution reactions of catalyst-loaded carbon electrodes in alkaline electrolyte solutions. The calibration constant, which correlates the mass signal of m/z = 44 to the partial current of the CO2 evolution reaction, is successfully obtained from the Faradaic current and the mass signal of CO stripping voltammetry. We analyze carbon corrosion reactions of Pt and metal oxide-loaded carbon electrodes to demonstrate the effectiveness of the constructed system. The corrosion behavior of the Pt-loaded carbon is similar to that in the acidic electrolytes except for the onset potential of the carbon corrosion. La0.6Ca0.4CoO3 and Ca2FeCoO5 show electrochemical carbon corrosion activity, while La0.4Sr0.6MnO3 does not show distinct electrochemical carbon corrosion activity.

ORR activity and stability of carbon supported Pt3Y thin films in PEMFCs

In order to investigate stability of oxygen reduction reaction (ORR) on a Pt3Y thin film under relevant fuel cell conditions, we performed an accelerated stress test (AST) consisting of 3600 potential cycles between 0.4 and 1.4 V at 1 V s−1 in a single proton exchange membrane fuel cell (PEMFC). The ORR activities were evaluated via polarization curves before and after the AST. Electrochemical active surface area (ECSA) was obtained by CO-stripping voltammetry whereas the morphological changes were monitored by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Variations in surface composition and electronic structures were evaluated by energy-dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS). After AST, the polarization curves show loss of ORR activity in all voltages for both Pt and Pt3Y. Except at very high voltages (E > 0.85 VRHE), the ORR activity of Pt3Y after AST is very close to that of Pt before AST. This correlates well with the results from the deconvolution of Pt-4f XPS spectra where the binding energy of metallic Pt in Pt3Y is comparable to pure Pt (71.22 eV). SEM and TEM images demonstrate that the morphologies of the aged Pt3Y and as-sputtered Pt are similar, whereas EDX results confirm a steady bulk composition of Pt3Y thin films throughout the entire electrochemical test. By correlating all these results, we conclude that the loss of ORR activity for Pt3Y is due to an increase in the thickness of the Pt overlayer which induces a relaxation of the Pt overlayer decreasing the compressive strain effect. For pure Pt, the loss of ORR activity is associated with a growth of the Pt domains associated with Ostwald ripening process.

Modulating the Interfacial Water Network of Dual-Site Pd/FeOx/C Catalyst for Efficient Formate Electrooxidation.

The rational design of electrocatalysts for formate oxidation reaction (FOR) in alkaline media is crucial to promote the practical applications of direct formate fuel cells (DFFCs). The FOR kinetic on palladium (Pd) based electrocatalysts is strongly hindered by unfavorably adsorbed hydrogen (Had) as the major intermediate species blocking the active sites. Herein, we report a strategy of modulating the interfacial water network of dual-site Pd/FeOx/C catalyst to significantly enhance the desorption kinetics of Had during FOR. Aberration-corrected electron microscopy and synchrotron characterizations revealed the successful construction of Pd/FeOx interfaces on carbon support as a dual-site electrocatalyst for FOR. Electrochemical tests and in situ Raman spectroscopy results showed that Had could be effectively removed from the active sites of the as-designed Pd/FeOx/C catalyst. CO-stripping voltammetry and density functional theory calculations (DFT) demonstrated that the introduced FeOx could effectively accelerate the dissociative adsorption of water molecules on active sites, which accordingly generates adsorbed hydroxyl species (OHad) to facilitate the removal of Had during FOR. This work provides a novel route to develop advanced FOR catalysts for fuel cell applications.

Hierarchical Pt-In Nanowires for Efficient Methanol Oxidation Electrocatalysis.

Direct methanol fuel cells (DMFC) have attracted increasing research interest recently; however, their output performance is severely hindered by the sluggish kinetics of the methanol oxidation reaction (MOR) at the anode. Herein, unique hierarchical Pt-In NWs with uneven surface and abundant high-index facets are developed as efficient MOR electrocatalysts in acidic electrolytes. The developed hierarchical Pt89In11 NWs exhibit high MOR mass activity and specific activity of 1.42 A mgPt-1 and 6.2 mA cm-2, which are 5.2 and 14.4 times those of Pt/C, respectively, outperforming most of the reported MORs. In chronoamperometry tests, the hierarchical Pt89In11 NWs demonstrate a longer half-life time than Pt/C, suggesting the better CO tolerance of Pt89In11 NWs. After stability, the MOR activity can be recovered by cycling. XPS, CV measurement and CO stripping voltammetry measurements demonstrate that the outstanding catalytic activity may be attributed to the facile removal of CO due to the presence of In site-adsorbing hydroxyl species.

Oxygen Reduction Reaction on Pt-Y/C Catalysts: Activity and Long-Term Stability Study

Pt-Y/C catalysts were prepared by a modified formic acid method and their structural characteristics and activity for oxygen reduction reaction (ORR) were evaluated. X-ray diffraction analysis showed that no alloy was formed between the metals and X-ray photoelectron spectroscopy (XPS) experiments showed that yttrium is presented as Y2O3, Y(OH)3 and Y-O-Pt species. CO stripping voltammetry and in situ X-ray absorption spectroscopy confirmed the interaction between Pt nanoparticles and yttrium species. The Pt-Y/C 7:3 material showed the higher specific activity (103 μA cmPt -2) for ORR. Following repetitive potential cycling, the activity for the ORR of the Pt-Y/C 7:3 catalyst declined in a similar proportion to the Pt/C material. Transmission electron microscopy analysis after stability for both catalysts showed that Pt/C particle size slightly increased and that for Pt-Y/C 7:3 remained the same. XPS made in ultrathin catalyst layer, agreeing with energy-dispersive X-ray spectroscopy analysis, revealed that the intensities of the Y 3d peaks were suppressed relative to the initial one and that yttrium in the form of Y2O3 and Y(OH)3 were dissolved, while the species Y-O-Pt still remain in the catalyst, maintaining the higher activity.

Investigation of Pt/Fe-N-C Hybrids Towards ORR in Acidic Environment

Polymer electrolyte membrane fuel cells (PEMFCs) are recognized as one of the renewable energy sources in portable, automobile, and stationary applications. Currently, both low temperature (LT) and high temperature (HT) PEMFCs use platinum group metal (PGM) based catalysts for oxygen reduction reaction (ORR) containing usually Pt nanoparticles on carbon black. To reduce the total cost of PEMFC stack, worldwide researchers have considerable attention to find an inexpensive alternative catalyst. Recently, metal-nitrogen-carbon (M-N-C) compounds such as Fe-N-Cs are the most promising PGM-free catalysts for ORR. However, they suffer from insufficient volumetric activity and electrochemical stability in PEMFCs. [1,2] Xiao et al. have proven an improved electrochemical stability of Pt-Fe-N-C electrocatalysts consisting of atomically dispersed Pt and Fe atoms or Pt-Fe alloy nanoparticles in comparison with Fe-N-C only. [3] Mechler et al. have reported that the addition of 1-2 wt.% Pt in hybrid Pt/Fe-N-C catalyst performs well with an increased stability in LT-PEMFCs. [4] Liao et al. have recently shown better ORR activity of Pt/Fe-N-C than Pt/C. [5] With the overriding goal of reducing LT- and HT-PEMFC production costs, Pt/Fe-N-C activity, selectivity and stability with systematically reducing the Pt-content has not been investigated yet. In this study, Pt/Fe-N-C hybrids are synthesized using PMF-011904 from Pajarito Powder (USA) as catalyst support and wet-chemically precipitated Pt nanoparticles with targeted Pt-contents of 40, 5, 1 and 0 wt.%. First, ICP mass spectrometry is used for Pt quantification along all catalysts, and transmission electron microscopy is carried out to investigate morphology and Pt nanoparticle diameter and distribution on the Fe-N-C catalyst. Second, ORR activity and selectivity is investigated by rotating ring disc electrode (RRDE) experiments in 0.1 mol L-1 HClO4, and electrochemical surface area of Pt is calculated by hydrogen underpotential deposition and CO stripping voltammetry. Last, accelerated stress testing (AST) is performed with 5,000 triangle potential cycles between 0.6–1.5 VRHE to evaluate the catalyst stability. Figure 1 shows the initial ORR curves during the RRDE experiments. The mass activities of 40, 5 and 1 wt.% Pt/Fe-N-C determined at 0.9 VRHE are 222.5 ± 41.2 A gPt -1, 170.8 ± 80.4 A gPt -1 and 49.0 ± 8.6 A gPt -1, respectively. Thus, the mass activity depends on Pt-content in the hybrid catalyst strongly. In addition, the other electrochemical characterization results are also going to be discussed in terms of catalyst selectivity, stability and the correlation with morphological aspects during the presentation. Figure 1 ORR curves in O2-saturated 0.1 mol L-1 HClO4 electrolyte with rotation speed of 1,600 rpm and scan rate of 5 mV s-1 (averaged results of three separate electrodes per each catalyst).[1] Y. He, S. Liu, C. Priest, Q.Shi , G. Wu, Chem. Soc. Rev. 2020, 11, 3484–3524.[2] T. Reshetenko, A. Serov, M. Odgaard, G. Randolf, L. Osmieri, A. Kulikovsky, Electrochem. Commun. 2020, 118, 106795.[3] F. Xiao, G.-L. Xu, C.-J. Sun, I. Hwang, M. Xu, H.-W. Wu, Z. Wei, X. Pan, K. Amine, M. Shao, Nano Energy 2020, 77, 10592.[4] A. K. Mechler, N. R. Sahraie, V. Armel, A. Zitolo, M. T. Sougrati, J. N. Schwämmlein, D. J. Jones, F. Jaouen, J. Electrochem. Soc. 2018, 165, F1084.[5] W. Liao, S. Zhou, Z. Wang, F. Liu, H. Pan, T. Xie, Q. Wang, ChemCatChem 2021, 13, 23, 4925-4930. Figure 1

Operando X-Ray Absorption Spectroscopic Study on Influence of Specific Adsorption of Sulfo Group in Perfluorosulfonic Acid Ionomer Towards ORR Activity of Pt/C Catalyst

Polymer electrolyte fuel cells (PEFCs) are clean energy devices with polymer electrolytes and are expected to play an important role in the development of a global renewable energy system and a pure hydrogen energy society in the future. PEFCs have already been applied for small-scale energy systems such as fuel cell vehicles (FCVs). Pt-based catalysts are basically used due to the relatively inefficient reaction kinetics and catalyst degradation under strong acidic conditions during the oxygen reduction reaction (ORR). However, there are still many difficulties in realizing acceptable cost-effective FCVs. It is known that the ORR activity of Pt-based catalysts is reduced by specific adsorption of anionic species. Perfluorosulfonic acid ionomers such as Nafion® are commonly included in the catalyst layers of PEFCs to provide protonic pathways for promoting the ORR1. However, direct observation of anion adsorption on practical Pt nanoparticle/C catalysts for perfluorosulfonic acid ionomers using X-ray absorption spectroscopy (XAS) still has less report. In this study, to achieve specific adsorption over a higher potential range that is at least equal to the ORR active potential (around 0.90 V vs. RHE), operando XAS measurements were performed; the electronic status and local structural change of Pt atoms induced by the specific adsorption of anions at any potential were observed2.Pt/C (29.1 wt.%; TEC10V30E) catalyst supported was purchased from TKK. Nafion® solution was employed to prepare Pt/C catalyst ink with I/C ranging from 0.0 to 1.0. And the amount of Pt/C was adjusted to form a 20 µgcarbon cm-2 catalyst layer after dropping 10 μL on a glassy carbon RDE. The electrochemical cell was constructed using a model electrode fabricated in the working electrode, a Pt mesh for the counter electrode, a reversible hydrogen electrode for the reference electrode, and 0.1 M HClO4 aq for the electrolyte. operando XAS measurement of Pt L-edge was carried out in SPring-8 (Japan).The specific activity decreased as the I/C ratio increased from 0.0 to 0.20. We utilized many methods to evaluate the adsorption species separately, including the measurements of ECSA and oxygen coverage, CO stripping voltammetry, operando X-ray absorption fine structure, and analysis of 5d orbital vacancy. The ECSA and oxygen coverage did not change with increasing ionomer content, indicating that the Pt/C catalyst activity was affected by other adsorption species. A comparison of the CO displacement charge and 5d orbital vacancies of the Pt/C catalysts with I/C = 0.0 and 1.0 suggests that the ionomer-specific adsorption increases when the I/C ratio of the Pt/C catalyst is 1.0; active sites on the surface of the Pt/C catalyst are occupied, resulting in lower catalyst activity. Acknowledgment This work was supported by the project (JPNP20003) and a NEDO FC-Platform project commissioned by the New Energy and Industrial Technology Development Organization (NEDO).

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

The application of proton exchange membrane fuel cells (PEMFCs) in light-duty vehicles (LDV) has dominated the fuel cell research field for the past decades. To reduce the LDV FC system cost to 30 $/kW by 2025 has driven the search for highly active cathode catalysts that could substitute the costly state-of-the-art Pt-alloy catalysts or reduce the cathode loadings to < 0.125 mgPt/cm2.1, 2 As novel ORR catalyst continue to emerge, theoretical calculations have turned the attention on Pt-rare earth (RE) alloys, such as platinum-yttrium alloys that were suggested to have superior activity for the oxygen reduction reaction (ORR) and superior long-term stability compared to conventional carbon-supported platinum catalyst (Pt/C). 3 Based on these findings, many attempts have been made to produce high electrochemical surface area (ECSA) Pt-RE alloy catalysts.4 In recent years, Hu, et al. introduced a new synthesis procedure that utilizes a carboiimide-assisted synthesis for the preparation of Pt-RE/C catalysts with an unprecedentedly high ECSAs in the range of ~50-60 m2/gPt.5 With such high ECSA PtxY/C catalysts, good PEMFC performance would be expected, but to date the ORR activity and stability of such PtxY/C catalysts has not been demonstrated in a PEMFC environment.In view of this, we reproduced the synthesis reported by Hu et al. using a Ketjen Black (KB) carbon support. The resulting PtxY/KB catalyst was characterized by X-ray diffraction, X-ray spectroscopy (EDS) in scanning transmission electron microscopy (STEM), and elemental analysis, indicating the formation of a Pt-richshell/Pt3Ycore structure that was caused by the acid washing procedure introduced before the electrochemical characterization.5 In our present study, two different Pt/KB catalysts were selected as reference materials: i) a Johnson Matthey reference catalyst consisting of small well-dispersed Pt nanoparticles on a KB support (Pt/KB-JM); ii) an in-house synthesized Pt/KB catalyst (Pt/KB-syn.) with a similar particle size distribution and ECSA as the in-house synthesized PtxY/KB catalyst (PtxY/KB-syn.). The ECSA (via CO-stripping voltammetry) and the ORR mass activity at 0.9 V vs. RHE (imass 0.9 V) of these three catalysts were first evaluated by rotating disk electrode (RDE) measurements in 0.1 M HClO4 at 25 °C. The catalysts were also incorporated as cathode catalysts in membrane electrode assemblies (MEAs), first determining their ECSA (by CO-stripping) and then their H2/O2 and H2/air performance in a 5 cm2 single-cell PEMFC hardware at 80 °C under differential flow conditions, including a quantification of the ORR mass activity at 0.9 V vs. RHE at 100 kPa O2.As can be seen in Figure 1, the relative ECSA and ORR mass activity values of the three different catalysts obtained in the RDE and the PEMFC configuration were essentially identical when evaluated at the same ionomer to carbon ratio (I/C = 0.7, g/g). Furthermore, a comparison of the RDE ORR activity at two different I/C ratios showed that the PtxY/KB-syn. and Pt/KB-syn. catalysts were more susceptible to ionomer poisoning when compared to the Pt/KB-JM catalyst. Following the approach taken in our previous publications, the voltage-cycling stability of the synthesized catalysts was also evaluated using an accelerated stress test (AST) consisting of a triangular potential scan between 0.6 and 1.0 VRHE at 50 mV/s up to 30000 cycles.5 Overall, the RDE and PEMFC data showed that the here synthesized carbon-supported Pt-richshell/Pt3Ycore catalyst does not shown an enhanced ORR activity nor a long-term stability benefit when compared to a Pt/KB catalyst with the same ECSA, contrary to what had been hypothesized earlier.3 References R. L. Borup, A. Kusoglu, K. C. Neyerlin, R. Mukundan, R. K. Ahluwalia, D. A. Cullen, K. L. More, A. Z. Weber and D. J. Myers, Current Opinion in Electrochemistry, 21, 192–200 (2020).M. Escudero-Escribano, K. D. Jensen and A. W. Jensen, Current Opinion in Electrochemistry, 8, 135–146 (2018).J. Greeley, I. E. L. Stephens, A. S. Bondarenko, T. P. Johansson, H. A. Hansen, T. F. Jaramillo, J. Rossmeisl, I. Chorkendorff and J. K. Nørskov, Nature Chemistry, 1(7), 552–556 (2009).J. N. Schwämmlein, G. S. Harzer, P. Pfändner, A. Blankenship, H. A. El-Sayed, and H. A. Gasteiger, Journal of the Electrochemical Society(165 (15)), J3173-J3185 (2018).Y. Hu, J. O. Jensen, L. N. Cleemann, B. A. Brandes and Q. Li, Journal of the American Chemical Society, 142, 953–961 (2020). Acknowledgment This work has been supported by the Fuel Cells and Hydrogen 2 Joint Undertaking under grant agreement No. 826097 (GAIA). This Joint Undertaking receives support from the European Union’s Horizon 2020 research and innovation programme, Hydrogen Europe and Hydrogen Europe Research. Figure 1

Nitrogen-doped carbon black supported synergistic palladium single atoms and nanoparticles for electrocatalytic oxidation of methanol

For commercially viable direct methanol fuel cells, electrocatalysts play a crucial role in motivating the sluggish methanol oxidation reaction (MOR) over anode. Unfortunately, the large-scale applications of current MOR catalysts are hampered by their poor tolerance to poisoning and fast activity degradation. Herein, a unique composite catalyst comprised of partial Pd nanoparticles and partial Pd single atoms (PdNPs/Pd-Nx@C) is developed. The as-fabricated catalyst exhibits remarkable activity of 9.45 mA·cm−2 towards MOR in alkaline solution, which is 7.05 and 3.92 times that of commercial Pd/C and nanoparticle type (PdNPs@C) electrocatalysts, respectively. Impressively, the PdNPs/Pd-Nx@C shows the highest long-time stability with 90.38% and 89.8% of the initial activity retained after 3600 s chronoamperometry (CA) test and 2000 cycles of cyclic voltammetry (CV) measurements with accelerated durability test (ADT), respectively. Combined with high-angle annular darkfield scanning transmission electron microscopy (HAADF-STEM), X-ray adsorption fine structure (XAFS) spectra and X-ray photoelectron spectroscopy (XPS) analyses, the superior performance of PdNPs/Pd-Nx@C can be ascribed to the synergistic effect from the Pd single atoms, N-doped carbon supports and Pd nanoparticles. Notably, the embedded Pd single atoms are liable to transfer electrons to the substrate due to the electronic metal-support interactions (EMSI) and the charge transfer between Pd nanoparticles and carbon supports is suppressed, inducing a weak adsorption strength of poisonous carbonous intermediate species on active Pd nanoparticles and improved poisoning tolerance in MOR process, which is verified by density functional theory (DFT) calculations as well as CO-stripping voltammetry experiments. This work not only contributes the first example of a synergistic catalyst between nanoparticles and single atoms for MOR but also deepens the knowledge on the metal-support interaction.

Sulphonated melamine polymer for enhancing the oxygen reduction reaction activity and stability of a Pt catalyst

• Poly(melamine) sulphonate enhances the oxygen reduction activity of Pt catalysts. • The enhancement of the activity persists even after a deterioration test at 79 °C. • The melamine polymer suppresses the degradation of Pt nanoparticles. Poly(melamine) sulphonate (Poly-MS) adsorbed on the surface of Pt nanoparticles enhanced the activity of Pt/C in the oxygen reduction reaction (ORR). This enhancement persisted even after an accelerated deterioration test (ADT) at 79 °C. Analysis of the particle size distribution using transmission electron microscopy (TEM) clearly showed that Poly-MS enhanced the stability of the Pt nanoparticles, enabling them to withstand the conditions of the ADT. These findings were supported by CO stripping voltammetry analysis.

Intercalated Gold Nanoparticle in 2D Palladium Nanosheet Avoiding CO Poisoning for Formate Production under a Wide Potential Window.

The electrochemical CO2 reduction into formate acid over Pd-based catalysts under a wide potential window is a challenging task; CO poisoning commonly occurring on the vulnerable surface of Pd must be overcome. Herein, we designed a two-dimensional (2D) AuNP-in-PdNS electrocatalyst, in which the Au nanoparticles are intercalated in Pd nanosheets, for formate production under a wide potential window from -0.1 to -0.7 V versus a reversible hydrogen electrode. Based on the X-ray absorption spectra (XAS) characterizations, CO accumulation detection, and CO stripping voltammetry measurements, we observed that the intercalated Au nanoparticles could effectively avoid the CO formation and boost the formate production on the Pd nanosheet surface by regulating its electronic structure.