Increase In Electrochemical Surface Area Research Articles

Toward Finding the Role of Surface Iron Ions in Enhancing Oxygen-Evolution Reaction.

The oxygen evolution reaction (OER) in alkaline media is crucial for energy conversion technologies, and Fe-based catalysts have garnered significant attention for their efficacy. In this study, we provide an investigation of Fe-based catalysts under OER conditions using some techniques. Our findings reveal minimal structural alterations in the bulk FeHxOy framework during OER, indicating that the bulk structure remains largely intact. Instead, the catalytic activity is primarily localized on the material's surface. This conclusion is corroborated by the measured low electrochemical surface area (ECSA) of FeHxOy, suggesting that its limited OER performance stems from a paucity of active sites rather than low intrinsic activity. The superior efficiency of Fe ions in conductive oxides or on conductive metal substrates (e.g., copper and gold) in OER is attributed to the increased availability of surface-active sites in these systems. To further elucidate this phenomenon, we investigated two additional systems: NiFe and VFe (hydr)oxides. For NiFe (hydr)oxides, we demonstrate that only surface Fe ions contribute actively to OER. In contrast, in VFe (hydr)oxides, the removal of vanadium resulted in a marked increase in ECSA and the generation of defect sites, significantly enhancing OER activity. These findings provide critical insights into the surface-specific role of Fe ions in catalytic activity and could inform future design strategies for more efficient OER catalysts by optimizing the availability and reactivity of surface-active Fe sites.

Single step grown porous polycrystalline nickel microstructures with ultra-thin defect rich surface oxide for alkaline water oxidation

Investigation on the intrinsic catalytic activity of structurally diverse polycrystalline nickel microstructures such as porous nickel sheets (PNS), porous folded/curled nickel structures (PFNS) and porous nickel balls (PNB) revealed the surface bounded electrocatalytic activities within an alkaline reaction environment for water oxidation. Nickel microstructures were grown via template/surfactant-free, single step solution combustion technique in air atmosphere. The distinct morphologies (porous nickel sheets, porous folded/curled nickel structures and porous nickel balls) were achieved through changing the quantity of HNO3 in the reaction mixture. The physicochemical characterisations were done with XRD, FESEM, EDS and XPS. Microscopic studies revealed the growth of nickel grains with numerous macro pores forming microstructures in distinct morphologies. The O ls spectra of XPS studies revealed the presence of O−/O2− sites and Ni 2p spectra were distinguished between the formation of Ni0/Ni2+/Ni3+ states, implied the existence of surface oxide with plenty of defects. The synergistic effect results from the formation of microscopic porous architectures with defect rich surface oxide on the electrochemical behaviour and OER activity of PNS, PFNS and PNB were discussed with electrochemical techniques such as CV, LSV, EIS and CP. The OER kinetics in terms of relatively low value of overpotential at 10 mA cm−2 and Tafel slope along with high specific activity of PNS/GCE with respect to PFNS/GCE and PNB/GCE were attributed to the combined effect of increase in electrochemical surface area, high roughness factor and fast charge transfer kinetics. The better electrochemical performance and OER activities of porous nickel sheets in comparison with folded/curled nickel structures and nickel balls is contributed to the unique 2D porous architecture with plenty of oxygen vacancies. This structure not only expose more surface for the formation of passive oxide layer in an alkaline reaction environment but also exhibit facile charge transport properties, causes the generation of numerous surface-active sites for electrocatalytic water oxidation. The outcome of our work gives new insights on the surface electrochemistry of polycrystalline nickel, enables micro-structuring as a prospective strategy towards the optimization of electrocatalysts as anode material for alkaline water oxidation.

Electrochemical studies on chromium doped SrTiO3 for supercapacitor applications

Perovskite oxides have garnered significant attention as potential active materials for supercapacitor applications. Recently, metal-doped perovskite oxides have gained prominence due to their potential to provide a synergistic blend of electrical conductivity, substantial electrochemical active surface area, and robust electrochemical activity. In this study, we systematically investigate the electrochemical properties of strontium titanate oxide (SrTiO3, STO) and chromium-doped strontium titanate oxide (Cr-STO), synthesized via the solid-state reaction method. Various material characterization techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS), are employed to examine the crystal structure, morphology, and chemical composition of these samples. Notably, Cr-STO demonstrates an approximately twentyfold increase in electrochemical surface area compared to pristine STO, resulting in enhanced anion storage capabilities when employed in alkaline 3 M KOH aqueous electrolytes. Detailed electrochemical kinetic studies reveal an augmented pseudocapacitive behavior in Cr-STO, with a more pronounced diffusive nature compared to pristine STO. Furthermore, symmetric supercapacitors fabricated with Cr-STO electrodes exhibit excellent electrochemical performance, maintaining over 93 % of their initial capacity after 10,000 charge-discharge cycles at a current density of 1 A g−1. These findings highlight the significant potential of chromium-doped strontium titanate oxide as a valuable contribution to the ongoing pursuit of novel material for supercapacitors.

High entropy molybdate-derived FeOOH catalyzes oxygen evolution reaction in alkaline media

High-entropy materials are a new class of materials that have lately been developed and applied to a variety of potential fields. Here we present that electrochemical activation facilitates the application of high-entropy molybdates (HEMo) as oxygen evolution catalysts in alkaline media. The activated HEMo delivers 10 mA cm−2 at a lower overpotential by 75 mV than the pristine HEMo and exhibits the Tafel slope as low as 45 mV dec−1. In particular, no significant decrease in activity is observed during 24 h of electrolysis. Operando Raman spectroscopy reveals that NiOOH is the dominating active phase under OER conditions for the pristine HEMo, while FeOOH is predominant for the activated HEMo. Therefore, the origin of the enhanced OER performance is likely attributed to the change in active sites from Ni to Fe as well as the increase in electrochemical surface area after activation. This work provides an application of HEMo to electrocatalysis, a design approach for the synthesis of nanoparticles containing multiple cations, and valuable insights into FeOOH as an active OER catalyst.

Kinetic relevancy of surface defects and heteroatom functionalities of carbon electrodes for the vanadium redox reactions in flow batteries

Heteroatom doping of carbon electrodes is an extensively practiced approach to enhance electrokinetics of vanadium redox reactions in flow batteries, because the doped heteroatom functionalities are conventionally considered as the catalytic active sites. In this study, we conducted p type (boron), n type (nitrogen or oxygen), and p-n type (boron and nitrogen) heteroatom doping on graphite felt electrodes, and thoroughly studied their intrinsic electrokinetic effects by collective and quantitative structure-property correlation analysis. The studies reveal that the apparent kinetic enhancements observed by the p type and the n type heteroatom doping are primarily due to the surface lattice defects on carbon electrodes rather than the furnished heteroatom functionalities. Markedly, however, the B and N co-doping give rise to exceptional enhancements in the intrinsic vanadium redox kinetics, both for the VO2+/VO2+ and V2+/V3+ redox reactions, with 2–4 fold greater electrocatalytic activities than those predicted by the increase of electrochemical surface area by the surface lattice defects. Consequently, the p-n type B and N co-doped GF electrodes offers significant enhancements in the efficiency and energy storage capacity of the vanadium redox flow battery that cannot be achieved by the p type (B) or the n type (N and O) heteroatom doping.

Gold Nanospikes Formation on Screen-Printed Carbon Electrode through Electrodeposition Method for Non-Enzymatic Electrochemical Sensor

In this study, we reported the construction of Gold Nanospike (AuNS) structures on the surface of screen-printed carbon electrode (SPCE) used for non-enzymatic electrochemical detection. This modification was prepared with a one-step electrodeposition method by controlling the electrodeposition parameters, such as applied potential and deposition time, via Constant Potential Amperometry (CPA). Those parameters and precursor solution concentration were varied to investigate the optimum electrodeposition configuration. The results confirmed that AuNS were homogenously deposited and well-dispersed on the working electrode surface of SPCE. The AuNS-modified SPCE was implemented as a non-enzymatic sensor toward dopamine and could enhance the electrocatalytic ability compared with the bare SPCE. Further examination shows that the sensing performance of the AuNS-modified SPCE produced an increase in electrochemical surface area (ECSA) at 17.25 times higher than the bare electrode, a sensitivity of 0.056 µA mM−1 cm−2 with a wide linear range of 0.2–50 µM and a detection limit of 0.33 µM. In addition, AuNS-modified SPCE can selectively detect dopamine among other interfering analytes such as ascorbic acid, urea, and uric acid, which commonly coexist in the body fluid. This work demonstrated that AuNS-modified SPCE is a prospective sensing platform for non-enzymatic dopamine detection.

Morphology restructuring: MOFs derived Ni3S2@FeCrMoSx/NF as a highly efficient and stable catalyst for water oxidation

Exploring low-cost and high-efficiency OER catalysts is still a challenge. In this paper, self-supporting catalyst-Ni3S2@FeCrMoSx/NF was prepared using metal organic frameworks as templates. The morphology of the pre-catalyst has been deeply restructured after the sulfidation reaction, which significantly changes the composition and catalytic performance of the catalyst. The overpotential of Ni3S2@FeCrMoSx/NF is only 144 mV and 241 mV at a current density of 10 and 50 mA cm−2 respectively, the Tafel slope is as low as 45 mV dec−1. And it can maintain good electrochemical stability at a high current density of 100 mA cm−2. The outstanding OER performance of Ni3S2@FeCrMoSx/NF can be attributed to the increase of electrochemical surface area after sulfidation, the synergistic effect among multi-metals and the synergistic effect of polymetallic sulfides generated by sulfidation.

(Digital Presentation) High-Temperature Ammonia Treatment for Carbon Felt Electrodes in All-Vanadium Redox Flow Batteries

Ammonia gas treatments of varying temperature were performed on carbon felt electrodes in this study. Their physical and electrochemical properties were investigated.Carbon felt electrodes are often used in vanadium redox flow batteries (VRFBs). Without processing, carbon felt has poor wettability which frustrates electrochemical activity. This material must be modified to improve performance, which has been historically accomplished with thermal treatments ostensibly to promote oxygen functional groups, although this has been the subject of debate as morphological impacts have also been observed. [1-3] Many attempts have been made to improve performance of carbon felt in VRFBs, but some of the more successful modifications have resulted in an increase in the specific surface area. [4-6] Previous research at the University of Tennessee Knoxville suggests edge sites play a role in improving performance. Preliminary experiments on carbon felt performed by this lab with ammonia at high temperatures have shown promising results. Additional experiments were performed at 900°C by varying length of treatment time, finding four hours to be optimal. [3] New experiments have been done to investigate the kinetic effects of temperature.For these experiments, commercially available carbon felts (SIGRACELL® GFD3 by SGL Carbon, Meitingen, Germany) were modified by exposure to flowing ammonia gas through a furnace at (500°C, 700°C, 900°C, and 1100°C) varying temperatures for four hours. The samples were tested in a single-cell flow battery using cyclic voltammetry (CV), polarization curves, and electrochemical impedance spectroscopy (EIS). This treatment results in a significant increase in electrochemical surface area and performance.The physical properties were characterized using scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), and Raman spectroscopy. This was done to study the mechanism and kinetic effects of ammonia on the carbon felt material as temperature increases during the treatment itself. Samples treated at the highest temperatures exhibited a notable loss of mass, which is observed in the SEM images in Figure 1. This resulted in a significant increase in edge sites and active surface area, along with a substantial increase in cell performance, which was achieved with the ammonia-modified carbon felts described in this work, with over three times the current density at 80% voltage efficiency compared to untreated felt. Sun, B. and M. Skyllas-Kazacos, Modification of graphite electrode materials for vanadium redox flow battery application—I. Thermal treatment.Electrochimica Acta, 1992. 37(7): p. 1253-1260.Pezeshki, A.M., "Impedance-Resolved Performance and Durability in Redox Flow Batteries. " PhD diss., University of Tennessee, 2016.Gass, K., High Performance Vanadium Redox Flow Battery Electrodes. [manuscript under submission], 2021.Lu, W., et al., High-performance porous uncharged membranes for vanadium flow battery applications created by tuning cohesive and swelling forces.Energy & Environmental Science, 2016. 9(7): p. 2319-2325.Zhou, X.L., et al., A high-performance dual-scale porous electrode for vanadium redox flow batteries.Journal of Power Sources, 2016. 325: p. 329-336.Wei, L., et al., Highly catalytic hollow Ti3C2Tx MXene spheres decorated graphite felt electrode for vanadium redox flow batteries.Energy Storage Materials, 2020. 25: p. 885-892. Figure 1. SEM images at 30,000X magnification of carbon felt electrodes: a) untreated, b) 4 hours NH3 treated at 500°C, c) 4 hours NH3 treated at 700°C, d) 4 hours NH3 treated at 1100°C. Scale was identical for all micrographs Figure 1

Rationally designed FeOx@CuOx/FTO dendritic hybrid: A sustainable electrocatalyst for efficient oxygen evolution reaction

The development of highly efficient and reliable electrocatalyst for oxygen evolution reaction is highly demanded by the energy conversion and storage devices. In this work, synergism effect of iron and copper is investigated for the oxygen evolution reaction. Here we reported the facile synthesis of microspheres of CuOx decorated with dendritic nanoarrays of FeOx (3% FeOx@CuOx) via spray coated on the FTO substrate used as an OER electrocatalyst. As oxides of copper (CuOx) are resistive to undergo oxidation, therefore act as strong platform where, heterostructures 3% FeOx@CuOx expose numerous active sites as well as the synergistic effect of copper and iron can catalyze the OER reaction at low overpotential and increases the durability of electrocatalyst as well. Moreover the optimization of Fe ions concentration mediate the electrochemical active surface area and intrinsic activity of electrocatalyst. Interestingly, it is found that after electrochemical oxidation by continuous CV cycling in 1.0 M KOH solution promotes the OER performance. The synthesized electrode obtain current density of 10 mAcm−2 and 80 mAcm−2 at low overpotential of 257 mV and 320 mV respectively, with small tafel slope (37 mVdec−1) for 3% FeOx@CuOx as compared to 3% FeOx@Cu2O. Moreover, the increase in electrochemical surface area and intrinsic activity of resultant material 3% FeOx@CuOx enhances considerably. Both experimental and computational studies indicate the auspicious surface properties for the adsorption and desorption of intermediates involved in the OER process. This can be attributed to the phase transformation of Cu2O to CuO during electrochemical oxidation process, changing the electronic structure of active sites which led to the generation of Oxides/hydroxides of iron and enhancing the Fe-O bonding, overall benefiting the OER process. The activity of optimized 3% FeOx@CuOx is comparable to the state of electrocatalyst RuO2.

Carbon Aerogel Based Thin Electrodes for Zero‐Gap all Vanadium Redox Flow Batteries – Quantifying the Factors Leading to Optimum Performance

AbstractDirect growth of resorcinol−formaldehyde carbon aerogels (CAGs) on carbon paper electrodes was achieved using a new approach. Materials with variations in density, mesoporosity and microporosity were prepared. Microstructural properties of the resultant thin electrodes are shown to directly influence performance in zero‐gap redox flow battery (RFB). BET analysis shows a total surface area between 643 to 931 m2 g−1. Deposition of only ≈15 wt.% CAG on the carbon electrode leads to a 320‐fold increase in electrochemical surface area. Analysis of the results saw a strong positive correlation of RFB performance with surface area. The best performing electrodes had a good balance between microporous and external surface area, and on the macroscopic scale had sufficiently large pores to allow efficient electrolyte permeation. The poorest performing electrodes which had the highest surface area, also had poor macroscopic porosity leading to large mass transport and solution resistance losses. The best performing electrodes were tested in a zero‐gap setup using polarization curves, showing a 25 % increase in power density at 100 mA cm−2 and a peak power density of 706 mW cm−2 at 1 V using thin electrodes.

Gas flow Stimulated Hydrodynamics for Preparation and Application of Platinized Titanium Hollow Fibre Electrodes

AbstractIn this study, Pt was electrodeposited on the surface of Ti hollow fibres from PtCl62− solution at fixed potential and at variable gas flow rate. Partial Pt coverage of Ti was obtained at flow rates≤5 mL⋅min−1, while a more‐even geometrical distribution and linearly increasing Electrochemical Surface Area (ECSA) of Pt was obtained for flow rates of >5 and <20 mL⋅min−1. Above 20 mL⋅min−1, the morphology did not significantly change, and only a limited increase in ECSA of Pt (PtECSA) was observed. Second, the performance of the Pt functionalized Ti‐HFEs was evaluated at fixed potential in i) liquid phase oxidation of FeII to FeIII, and ii) the hydrogen (gas) evolution reaction (HER). Generally, for the oxidation of Fe(CN)64−, a linear increase in current from 3 to ≈9 mA was found as a function of increasing gas flow rate. For the HER, a gas evolving reaction, initially (in the range of 0–10 mL⋅min−1) a much larger enhancement in current (from ≈‐10 to −35 mA) was observed than consecutively at higher flow rates. The effect of gas flow rate on Pt deposition, and utilization of platinized Ti HFEs, is explained on the basis of increasing fractional participation of relatively small pores at high flow rates, and generally an increasing mass transfer coefficient (kM) associated with localized mixing of the electrolyte near the electrode/electrolyte interface. The kM is roughly in the same order of magnitude as obtained in experiments using rotating disc electrodes.

Magnetized manganese-doped watermelon rind biochar as a novel low-cost catalyst for improving oxygen reduction reaction in microbial fuel cells

Microbial fuel cells (MFCs) are promising equipment for water treatment and power generation. The catalyst used in the oxygen reduction reaction (ORR) at the cathode is a critical factor for efficacy of MFCs. Therefore, it is important to develop cost-effective cathode catalysts to enhance application of MFCs. In the current study, a novel cathode catalyst was developed, which was annealed with watermelon rind as raw material and transition metals including iron, and manganese were introduced. The 700Mn/Fe@WRC catalyst, which was annealed at 700 °C, exhibited excellent electrochemical performance. The high relative content of pyridine nitrogen caused by the inherent nitrogen element of the watermelon rind and the high content of iron and manganese elements introduced resulted in increase in electrochemical surface area to 657.6 m2/g. The number of electrons transferred ORR was 3.96, indicating that ORR occurs through a four-electron pathway. The maximum power density of MFCs was 399.3 ± 7.4 mW/m2 with a fitting total internal resistance of 15.242 Ω, and the removal efficiency of COD was 97.1 ± 1.2%. The cost of the 700Mn/Fe@WRC catalyst was approximately 0.15 $/g, which is significantly lower compared with Pt/C (33.0 $/g). Experimental verification showed that the 700Mn/Fe@WRC prepared using the economical watermelon rind biochar (WRC) is an excellent substitute for non-precious metal catalysts used in MFCs.

Modifying Carbon Felt Electrodes Using High-Temperature Ammonia Treatment to Improve the Performance of All-Vanadium Redox Flow Batteries

High temperature ammonia treatments were performed on carbon felt electrodes in this study. Their physical and electrochemical properties were investigated.Carbon felt electrodes are often used in vanadium redox flow batteries (VRFBs). Without intervention, carbon felt has poor wettability which frustrates electrochemical activity. This material must be modified to make it more effective, which has been historically accomplished with thermal treatments to promote oxygen functional groups. [1] Many attempts have been made to improve performance of carbon felt in VRFBs, but some of the more successful modifications have resulted in an increase in the specific surface area. [2-4] Preliminary experiments on carbon felt performed by this lab with ammonia at high temperatures have shown promising results. [5]For our experiments, commercially available carbon felts (SIGRACELL® GFD3 by SGL Carbon, Meitingen, Germany) were modified by exposure to flowing ammonia gas through a furnace at 900°C for varying lengths of time. The samples were tested in a single-cell flow battery using cyclic voltammetry (CV), polarization curves, and electrochemical impedance spectroscopy (EIS). This treatment results in a significant increase in electrochemical surface area and performance.The physical properties were characterized using scanning electron microscopy (SEM), energy-dispersive x-ray spectroscopy (EDS), and Raman spectroscopy. A pitting effect was observed in SEM images, preceded by surface blistering at shorter lengths of exposure.Greatly increased active surface area, along with a substantial increase in cell performance, was achieved with the ammonia-modified carbon felts described in this work. Sun, B. and M. Skyllas-Kazacos, Modification of graphite electrode materials for vanadium redox flow battery application—I. Thermal treatment. Electrochimica Acta, 1992. 37(7): p. 1253-1260.Lu, W., et al., High-performance porous uncharged membranes for vanadium flow battery applications created by tuning cohesive and swelling forces. Energy & Environmental Science, 2016. 9(7): p. 2319-2325.Zhou, X.L., et al., A high-performance dual-scale porous electrode for vanadium redox flow batteries. Journal of Power Sources, 2016. 325: p. 329-336.Wei, L., et al., Highly catalytic hollow Ti3C2Tx MXene spheres decorated graphite felt electrode for vanadium redox flow batteries. Energy Storage Materials, 2020. 25: p. 885-892.Pezeshki, A.M., "Impedance-Resolved Performance and Durability in Redox Flow Batteries. " PhD diss., University of Tennessee, 2016. Figure 1

Boosted up stability and activity of oxygen vacancy enriched RuO2/MoO3 mixed oxide composite for oxygen evolution reaction

Iridium free, acidic-stable, cost-effective, and efficient oxygen evolution reaction (OER) electrocatalyst is considered to be the bottleneck in the quest for sustainable energy production/storage devices. RuO2 has been proved as a highly active and standard OER electrocatalyst with poor stability. Herein, we are successfully providing the facile approach to synthesize the mixed oxide composite of RuO2 tailored with MoO3. Fifty percent reduction of noble metal contents, two times enhanced activity and excellent durability as compared to pure homemade and commercial RuO2 have been confirmed by numerous characterization techniques. Enhanced electrochemical performance of best mixed oxide composite is observed due to increasing number of oxygen vacancies, electronic distortion, lower oxidation state of noble metal, and reduced value of the Tafel slope. Furthermore, the best composite shows the 7-fold increase in electrochemical surface area, 3.2 times improvement in the bulk mass activity, and less value of overpotential.

Facile synthesis of IrO2 nanoparticles decorated @ WO3 as mixed oxide composite for outperformed oxygen evolution reaction

Oxygen evolution reaction (OER) electrocatalysts play the critical role in efficiency and durability for different hydrogen production systems. We have successfully synthesized the earth abundant WO3 coupled with IrO2 as mixed oxide composite by a facile two-step chemical method. 50% reduction in noble metal contents (IW-50) followed by two times enhancement in activity, four-folds increase in bulk mass specific activity along with the stability of mixed oxide composite as compared to state –of –the art IrO2 catalyst are affirmed. Superior performance of mixed oxide composites are perceived due to four times increase in electrochemical surface area, reduction of Tafel slope, four-fold increase of turn over frequency, electronic distortion in Ir-4f spectrum of IW-50 along with the bridging of lattice oxygen atoms between iridium and tungsten metals. We believe that it would open up the new avenues for effective utilization of noble metal with high valence tungsten metal in corrosive environment.

Temperature Dependence of Degradation Processes in LT-PEMFC: Focus on Low Temperatures

Longevity is a key criterion for the future success of fuel cells in challenging markets like the automotive drive train as it contributes to cost and user experience. The analysis of degradation processes is therefore currently in the focus of research. It is known, that several degradation processes exist, which over time can cause the failure of LT-PEMFC. Examples are changes in the structure of the catalyst particles due to effects like platinum dissolution or Ostwald ripening, the loss of catalyst particles due to corrosion of the carbon support or thinning and pinhole formation of the membrane due to attack by radicals and other detrimental intermediates. A number of test protocols exists which try to selectively test for the influence of one particular degradation process. Thereby the different degradation processes are assigned to vehicle operation conditions as described e.g. by Ohma et al. for the Fuel Cell Commercialization Conference of Japan (FCCJ) test protocols1. Common assignments are e.g. the tests of platinum particle degradation to driving at variable loads as it is tested with voltage jumps between 0.6 V and 1.0 V or the membrane degradation to standby as it is tested by potential hold at OCV. The carbon corrosion tests, which usually are assigned to system start-stop and are performed by fast potential cycling between 1.0 V and 1.5 V. the assignment as well as the selected potential window is derived from the results of Reiser et al.2, who found very high potential for the transient situation that anode and cathode are both filled with air when hydrogen is admitted to the cathode for the system start. This situation also often referred to as air/air start, can indeed occur in the operation of an automotive fuel cell stack. However, as it is due to longer standstill of the vehicle, it will happen at the vehicle ambient temperature which is likely 20 °C or below. The effect of temperature on degradation processes at fuel cell catalyst and fuel cell membrane electrode assemblies has been studied before also by our group3 but usually with focus to elevated temperatures well above ambient temperature. Publication of results even on catalyst activity for the relevant temperature window between 0 °C and 20 °C are scarce and even less exist which include degradation effect. Here we will present on test series in which we studied a commercial Pt/C fuel cell catalysts, both at RDE and single cell level, in the temperature window between 0 °C and 20 °C. In Figure 1 results on the RDE measurement at different temperatures are depicted. As can be seen in figure 1 a), the direct effect of the temperature on the performance is simply a reduced activity without changes in the Tafel slopes. If the carbon corrosion test is performed at different temperatures the change of the electrochemical surface area (ECSA) determined by evaluation of the HUPD part of the CV differs for the different temperatures. At all temperatures the carbon corrosion test causes a slight increase in ECSA following the first sets of stress cycles followed by a severe decay. Now, at lower temperatures this initial increase is stronger and endures longer than at 20 °C. Also the final decay is much more important at 20 °C than at 10 °C or 0 °C. In contrast to this finding, the kinetic current density at 0.9 V after the entire set of 20.000 cycles shows a stronger increase at 20 °C than at the lower temperatures (cf. figure 1 c). As the current density after the stress cycles is normalised to the remaining surface area, it means that the remaining catalyst has a higher activity. In this context, the results of the CO stripping before and after the stress tests shown in figure 1 d) are of interest. Here it is found that the carbon corrosion tests cause the evolution of a pre-peak oxidation area for CO which according to Maillard et al.4 is indicating the presence of particle agglomerates. This behaviour is much lower if the stress test is performed at lower temperatures. In the presentation further results, including test on commercial Pt3Co/C catalyst and single cell tests will be reported. A. Ohma, K. Shinohara, A. Iiyama, T. Yoshida, and A. Daimaru, ECS Trans., 41(1), 775–784 (2011)C. A. Reiser et al., Electrochem. Solid-State Lett., 8, A273–A276 (2005)C. Cremers et al., J. Electrochem. Soc., 165 (2018)F. Maillard et al., Phys. Chem. Chem. Phys., 7, 385–393 (2005) Figure 1

NiSe2 nanocrystals anchored graphene nanosheets as highly efficient and stable electrocatalyst for hydrogen evolution reaction in alkaline medium

A NiSe2/reduced graphene oxide (rGO) hybrid, constructed by NiSe2 nanocrystals homogeneously anchored on the rGO nanosheets, is fabricated through a facile one-step low-temperature solvothermal synthesis. Compared with the bare NiSe2 counterpart, the NiSe2/rGO hybrid delivers much better hydrogen evolution reaction (HER) performance with a low Tafel slope of 68.8 mV dec−1 and low onset potential of −149 mV in 1 M KOH. In addition, the overpotential of the hybrid for 120 mA cm−2 is only 404 mV, which is comparable to that of Pt/C catalyst (375 mV). Moreover, the alkaline electrocatalytic activity of the NiSe2/rGO hybrid is stable even after testing for 20 h. The outstanding electrocatalytic activity and high stability of NiSe2/rGO hybrid are in close link with its unique structure: NiSe2 nanocrystals with uniform crystal size are evenly distributed and coherently anchored on the two-dimensional matrix of rGO nanosheets, resulting in significant increase in electrochemical surface area and the number of catalytic active sites; the rGO nanosheets constitute a highly conductive network to facilitate the charge transfer. This work presents a high-efficiency, stable and cost-effective electrocatalyst for HER in alkaline medium.

A comparative study on catalytic activity and stability of TiO2, TiN, and TiC supported Pt electrocatalysts for oxygen reduction reaction in proton exchange membrane fuel cells environment

The serious corrosion of carbon support in the Pt-based catalysts, resulting in their instability, is one of the most important technical issues hampering the wide application of proton exchange membrane fuel cells (PEMFCs). In order to address this issue, TiO2, TiN, and TiC supported Pt nanoparticles (NPs) catalysts were synthesized using a simple polyol process and their oxygen reduction reaction (ORR) activity and durability have been investigated in acidic media of PEMFCs using rotating disk electrode (RDE) technique and compared with the commercial carbon supported Pt catalyst. The average Pt NPs sizes are 2.3, 2.3, and 2.6nm for the Pt/TiO2, Pt/TiN, and Pt/TiC catalysts, respectively. Among these three synthesized catalysts, the Pt/TiC catalyst has the highest stability and best catalytic performance with higher ORR current, electrochemical surface area (ECSA) and mass-specific activity. The ORR performance of the synthesized Pt/TiC catalyst is found to be promising with higher area-specific activity (Is) of 252.6 μA cmPt−2 and almost identical mass-specific activity (Im) of 0.16 A mgPt−1 than that of the Pt/C with Is of 235.5 μA cmPt−2 and Im of 0.17 A mgPt−1 at E=0.9V in 0.1M HClO4 solution. Additionally, the Pt/TiC shows the outstanding stability with no reduction in ORR performance and 10.1% increase in ECSA after accelerated stress test (AST).

Durability of PtCo/C Cathode Catalyst Layers Subjected to Accelerated Stress Testing

The cost and durability of Polymer Electrolyte Membrane Fuel Cells (PEMFCs) are the two major barriers to the commercialization of these systems for stationary and transportation power applications.1 Given the stringent performance requirements that PEMFCs have to meet for automotive applications, Pt-alloy catalysts are being considered as cathode catalysts. While PtCox alloy catalysts exhibit better mass activity than Pt/C catalysts and can meet the beginning of life performance requirements, their durability is not proven. Several studies have indicated that the base metal leaches out of these catalysts over time and any benefits due to alloying is lost over the lifetime of the Membrane Electrode Assembly (MEA).2 The U.S. DOE Fuel Cell Tech Team has recommended various ASTs for PEMFC components.3,4 Los Alamos National Laboratory (LANL) has previously reported on the durability of several Pt/C catalysts during both simulated drive cycle testing and accelerated stress tests (ASTs).5 A catalyst AST that involved applying a square wave with 3 sec at 0.6V and 3 sec at 0.95V was determined to be an appropriate AST for evaluating the durability of Pt electrocatalysts.6In this study the performance of PtCo/C cathode catalyst based MEAs subjected to this AST were evaluated. The durability of PtCo/C catalysts was found to be comparable or better than that of the Pt/C based catalysts. Moreover the activity of the PtCo/C catalyst based MEA was also enhanced with respect to the Pt/C MEA. Figure 1 illustrates the evolution of the electrochemical surface area (ECSA) over 30,000 cycles of the square wave AST. The PtCo/C based MEA exhibited little change in ECSA over the course of the test. The ECSA initially increased due to insufficient conditioning and then decreasing due to catalyst particle size increase. In contrast, the Pt/C catalyst showed significant increase in ECSA over the course of the test. Finally the starting ECSA of the PtCo/C catalyst based MEA was significantly lower than that of the Pt/C MEA, while the end of test (EOT) ECSA was almost identical. These results are consistent with the small (≈ 2nm) starting particle size of the Pt and relatively large (≈ 5nm) starting particle size of the PtCo catalyst. The performance of the two MEAs before and after the durability AST is presented in Figure 2. It should be noted that the Pt/C based MEA had a loading of 0.15mg.Pt/cm2 whereas the PtCo/C MEA had an initial loading of 0. 21mg.Pt/cm2. The beginning of test (BOT) performance of the PtCo/C based MEA was significantly better in the kinetic region due to both the alloying effect and higher Pt loading. However, the BOT performance of the Pt/C MEA was better in the mass transport region due to extra mass transport limitations observed in alloy catalysts. The End of test (EOT) performance of the PtCo/C based MEA is only slightly higher than that of the EOT performance of the Pt/C based MEA, consistent with the fact that most of the Co has leached out of the PtCo catalyst. In this presentation the durability implications of using PtCo alloy catalysts will be discussed in detail with results presented from TEM, SEM, XRF, XRD and electrochemical testing.

Approaches towards Improving the Dispersion of Electrodeposited Palladium on Carbon Supports

Palladium (Pd) was electrochemical deposition on activated carbon from chloride precursor in acid media. The effect of precursor concentration was studied in relation to the dispersion of Pd at a particular deposition potential, and the influence of support material such as conventional Vulcan XC-72R (VXC) and activated carbon prepared from Wood Apple Shell (WAS) on the dispersion of Pd is investigated. Scanning electron microscope images showed, changing the support from VXC to WAS carbon improved the dispersion of Pd, and CO stripping and hydrogen adsorption/desorption experiments displayed an increase in electrochemical surface area for Pd on WAS carbon support. Comparison of electrochemical data for oxygen reduction reaction and formic acid oxidation suggests that Pd deposited on wood apple shell (WAS) carbon showed higher activities relative to Pd deposition on Vulcan. Cyclic and linear sweep voltammetry results showed a positive shift in onset potential up to 80mV towards oxidation and reduction reactions on changing the support to WAS carbon. The effectiveness of improving the utilization of Pd by changing the support from VXC to WAS activated carbon is discussed in detail.