Long-term Electrolysis Research Articles

Role of Structural and Compositional Changes of Cu2O Nanocubes in Nitrate Electroreduction to Ammonia.

Nitrate electroreduction reaction (NO3RR) to ammonia (NH3) still faces fundamental and technological challenges. While Cu-based catalysts have been widely explored, their activity and stability relationship are still not fully understood. Here, we systematically monitored the dynamic alterations in the chemical and morphological characteristics of Cu2O nanocubes (NCs) during NO3RR in an alkaline electrolyte. In 1 h of electrolysis from -0.10 to -0.60 V vs RHE, the electrocatalyst achieved the maximum NH3 faradaic efficiency (FE) and yield rate at -0.3 V (94% and 149 μmol h-1 cm-2, respectively). Similar efficiency could be found at a lower overpotential (-0.20 V vs RHE) in long-term electrolysis. At -0.20 V vs RHE, the catalyst FE increased from 73% in the first 2 h to ∼90% in 10 h of electrolysis. Electron microscopy revealed the loss of the cubic shape with the formation of sintered domains. In situ Raman, X-ray diffraction (XRD), and in situ Cu K-edge X-ray absorption near-edge spectroscopy (XANES) indicated the reduction of Cu2O to oxide-derived Cu0 (OD-Cu). Nevertheless, a remaining Cu2O phase was noticed after 1 h of electrolysis at -0.3 V vs RHE. This observation indicates that the activity and selectivity of the initially well-defined Cu2O NCs are not solely dependent on the initial structure. Instead, it underscores the emergence of an OD-Cu-rich surface, evolving from near-surface to underlying layers over time and playing a crucial role in the reaction pathways. By employing online differential electrochemical mass spectrometry (DEMS) and in situ Fourier transform infrared spectroscopy (FTIR), we experimentally probed the presence of key intermediates (NO and NH2OH) and byproducts of NO3RR (N2 and N2H x ) for NH3 formation. These results show a complex relationship between activity and stability of the nanostructured Cu2O oxide catalyst for NO3RR.

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

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

Designing and structuring MnO2 coating compositions for efficient and clean zinc electrowinning production

Lead-silver (Pb-Ag) anodes in the zinc electrolysis have resulted in significant environmental pollution and waste of valuable resources due to the influence of the lead corrosion reaction (LCR). Herein, the composition and interfacial structure of manganese dioxide (MnO2) coatings were designed and regulated by controlling the electrodeposition nucleation process using a Pb-Ag anode as the substrate. MnO2 coatings with a three-dimensional spherical bicrystalline-phase (β/γ) hydrophilic structure were synthesized. The introduction of γ-MnO2 not only increased the hydrophilicity of the coating, but also increased the content of the active substances Mn3+ and Oabs, thus improving the intrinsic OER activity of the MnO2 anode. Furthermore, density functional calculations have demonstrated that γ-MnO2 reduces the energy barrier of the determining step and increases the adsorption capacity of OH*, which is conducive to promoting the OER process. It was also demonstrated that the MnO2-coated anode could suppress the generation of Pb4+, thus inhibit the LCR process. Long-term electrolysis experiments have shown that the β/γ-MnO2 composite phase-coated anode can not only improve the oxygen evolution reaction (OER) rate and reduce energy consumption, but also effectively mitigate the generation of lead pollution and further reduce the impurity content of zinc products. This approach can simultaneously achieve economic benefits and environmental protection.

Ampere-Level Hydrogen Generation via 1000 H Stable Seawater Electrolysis Catalyzed by Pt-Cluster-Loaded NiFeCo Phosphide.

Seawater electrolysis can generate carbon-neutral hydrogen but its efficiency is hindered by the low mass activity and poor stability of commercial catalysts at industrial current densities. Herein, Pt nanoclusters are loaded on nickel-iron-cobalt phosphide nanosheets, with the obtained Pt@NiFeCo-P electrocatalyst exhibiting excellent hydrogen evolution reaction (HER) activity and stability in alkaline seawater at ampere-level current densities. The catalyst delivers an ultralow HER overpotential of 19.7mV at -10mA cm-2 in seawater-simulating alkaline solutions, along with a Pt-mass activity 20.8 times higher than Pt/C under the same conditions, while dropping to 8.3mV upon a five-fold NaCl concentrated natural seawater. Remarkably, Pt@NiFeCo-P offers stable operation for over 1000 h at 1 A cm-2 in an alkaline brine electrolyte, demonstrating its potential for efficient and long-term seawater electrolysis. X-ray photoelectron spectroscopy (XPS), in situ electrochemical impedance spectroscopy (EIS), and in situ Raman studies revealed fast electron and charge transfer from the NiFeCo-P substrate to Pt nanoclusters enabled by a strong metal-support interaction, which increased the coverage of H* and accelerated water dissociation on high valent Co sites. This study represents a significant advancement in the development of efficient and stable electrocatalysts with high mass activity for sustainable hydrogen generation from seawater.

Rapid electrodeposition synthesis of partially phosphorylated cobalt iron phosphate for application in seawater overall electrolysis

To obtain hydrogen energy from seawater, it is of utmost importance to design an efficient bifunctional electrocatalyst that can be produced on a large scale and in a rapid manner. In this work, iron cobalt phosphate (CoFe-EP/NF) for long-term efficient and stable seawater electrolysis were rapidly synthesized by a simple electrodeposition. The study showed that metal phosphides/phosphates provided additional active sites for the catalysts for hydrogen evolution reaction (HER, 160 mV at 100 mA/cm2) and oxygen evolution reaction (OER, 266 mV at 100 mA/cm2), in alkaline seawater electrolyte (1 M KOH + seawater), respectively. Notably, the presence of phosphate groups facilitates the transformation of cobalt-iron metal phosphates into the truly reactive substance CoOOH, which improves the OER kinetics. In addition, the phosphate layer formed after catalyst activation avoids the occurrence of chlorine evolution reaction (CER) by shielding the adsorption of Cl−, thus enhancing the corrosion resistance and enabling long-term stable operation in seawater. The two-electrode overall seawater electrolysis easily reaches 100 mA/cm2 at 1.68 V and exhibit a long-term durability of more than 100 h. This study offers a viable approach for the synthesis of electrocatalysts with high activity and corrosion resistance, which is vital for the practical realization of large-scale seawater electrolysis.

Controlled formation of CoOOH/Co(III)-MOF active phase for boosting electrocatalytic alkaline water oxidation

Surface reconstituted metal-organic frameworks (MOFs) offer appealing properties for electrocatalysis due to their unique structural and compositional advantages. In this work, a controlled potential-induced reconstruction of a two-dimensional cobalt metal-organic framework for boosting oxygen evolution reaction in alkaline media is reported. The current MOF is shown to undergo a partial structural transformation that generates a heterogeneous system, where the original MOF coexists with an oxyhydroxide phase. In fact, the potential-induced stabilization of Co(III) metal centers in the MOF is crucial for delaying its full degradation in alkaline media. This partial retention of the Co(III)MOF phase in the so-derived heterogeneous catalyst has been demonstrated to be decisive for boosting the alkaline electrocatalytic oxygen evolution reaction (OER), displaying superior OER activity in terms of both thermodynamic and kinetic merits compared to the benchmark IrO2 and RuO2 electrocatalysts and the prototypical cobalt (oxy)hydroxides, with a Tafel slope of 52 mV dec−1 and a turnover frequency (TOF) of 6.8 s−1 at 450 mV. Remarkably, the generated final product is stable, exhibiting high robustness and long durability for long-term OER electrolysis. This work provides new insight into the impact of the reconstruction of a MOF for alkaline OER under typical electrochemical conditions, which ultimately benefits the rational design of MOF-based catalysts with high electrocatalytic activity for oxidation reactions.

Electropolishing of Magnesium and Its Alloys using a Safe Glycol Solution containing Sodium Chloride

Abstract The electropolishing behavior of pure magnesium and its alloys in ethylene glycol (EG), diethylene glycol (DEG), triethylene glycol (TrEG), and tetraethylene glycol (TeEG) solutions containing sodium chloride was investigated using electrochemical measurements, microscopic observations, and reflectance measurements. Large light-grayish cloudy areas with micrometer-scale linear irregularities were formed on the magnesium surface via constant-voltage electrolysis in the EG solution, whereas mirror-finished magnesium surfaces were successfully obtained in the DEG and TeEG solutions. Among these, the DEG solution is considered appropriate for electropolishing because of its lower viscosity and market price. The reflectance of the entire visible wavelength region gradually increased with time during electrolysis in the DEG solution at 308 K. We found that short-term electrolysis for 3 min at the higher voltage of 75 V should be selected if a moderately polished surface is to be rapidly obtained, whereas long-term electrolysis for 60-300 min at 50 V should be performed if a highly polished surface with an extremely high reflectivity measuring more than 80% can be obtained. Three-dimensional magnesium specimens with curved and spiral shapes and an LZ91 magnesium alloy consisting of a simple solid-solution matrix can also be electropolished via electrolysis in a DEG solution.

Facile Synthesis of Ni(OH)2 through Low-Temperature N-Doping for Efficient Hydrogen Evolution

Nickel hydroxide is a potentially cheap non-precious metal catalytic material for alkaline hydrogen evolution reactions (HERs). Herein, a nickel form (NF)-based nitrogen-modified nickel hydroxide (N-Ni(OH)2/NF) with interlaced two-dimensional (2D) nanosheet structures was synthesized by a simple one-step ammonia vapor-phase hydrothermal method for efficient electrocatalytic HERs. The effect of the reaction temperature of the catalyst preparation on the HERs’ performance was studied in detail. The HER activity of N-Ni(OH)2/NF is enhanced by the large specific surface area, mass transfer and electron conductivity provided by a unique and suitable 2D nanostructure and nitrogen doping. The obtained N-Ni(OH)2/NF not only shows a superior HERs performance, but also exhibits good stability during long-term electrolysis.

Superaerophobic Ni3N/Ni@W2N3 multi-heterointerfacial nanoarrays for efficient alkaline electrocatalytic hydrogen evolution reaction

The hydrogen evolution performances of electrocatalysts are greatly restricted by their unfavorable hydrogen evolution kinetics and the undesirable accumulation of as-evolved gas bubbles on the electrocatalysts surface. Herein, we present the fabrication of self-supporting multi-heterointerfacial nanoarrays electrode toward addressing these challenges simultaneously. A monolith Ni3N/Ni@W2N3 electrode is prepared, which exhibits a multi-heterojunction interface between the different components. The construction of this multi-heterojunction interface allows for the redistribution of the electrons, thus alleviating the strong Ni-H bond and optimizing the hydrogen adsorption free energy toward more efficient HER catalysis. Moreover, by virtue of the distinct nanoarray structure, the Ni3N/Ni@W2N3 nanoarrays exhibit improved hydrophilicity and superaerophobicity compared with Ni/Ni3N, facilitating water contact and enabling more efficient detachment of the as-evolved H2 bubbles from the surface. Benefiting from these attractive features, the Ni3N/Ni@W2N3 nanoarrays deliver an attractive alkaline HER catalytic activity with a low overpotential of 66 mV to achieve a current density of 10 mA cm−2, which is comparable with that of the benchmark Pt/C electrode. Moreover, the electrode exhibits remarkable stability during long-term electrolysis. The simultaneous interface and nanostructure engineering provide a feasible pathway for obtaining high-performance electrodes and beyond for various electrochemical reactions.

Boosting Oxygen Electrocatalysis via Pre-Magnetized Multi Metallic Electrocatalyst

The quest for highly efficient durable and cost-effective electro catalysts for oxygen evolution reaction (OER) remains a pivotal focus in the advancement of renewable energy conversion technologies. Transition metal-based alkaline media electrocatalysts have emerged as promising candidates due to their versatile electronic structures and cost effectiveness. Among these, magneto-electrocatalysts, integrating magnetic properties with electrocatalytic functionalities, represent a novel frontier in OER research. In this study, we introduce a novel approach to enhance OER performance via the utilization of pre-magnetized multi-metallic (Fe-Ni-Co ) doped electrocatalysts, harnessing electron spin polarization. We tailored the electronic structure and magnetic properties of the catalyst, promoting and validating the principle of spin polarization for augmenting OER activity. Through a comprehensive experimental study, we have investigated how the inclusion of magnetic components influences the catalytic activity, stability, and overall efficiency of the electrocatalyst during OER. Experimental methodologies involving material synthesis, characterization techniques (XRD,FE-SEM, VSM study) and electrochemical analysis are employed to assess the structural, magnetic, and electrocatalytic properties of the synthesized pre-magnetised electrocatalyst.We employed the Fe-modified Nickel foam (NF) substrate as a catalyst support. Three distinct electrocatalysts (EC) [NF/Fe-Ni, NF/Fe-Co, and NF/Fe-NiCo] were electrodeposited in two different types: (electrodeposition without magnetic field) and (electrodeposition with applied magnetic field 0.6 T). Observations revealed that for all three electrocatalyst, the electrocatalysts [which were synthesized by applying a magenetic field during eletro deposition and later on OER activity was measured in the absence of magnetic field ] exhibit superior electrocatalytic activity towards OER compared to its counterparts . The highest electrocatalytic activity is provided by NF/Fe-NiCo of 0.5 mA/cm2 ECSA in the absence of a magnetic field and 0.533 mA/ cm2 ECSA in the presence of magnetic field. This is superior to that of the precious metal Ru, which has a specific activity of 0.49 mA/ cm2 ECSA at 1.5V (versus RHE). After analysing the OER performance of the catalyst, we found that the activity of NF/Fe-NiCo improved from 69.15 to 89.55 mA/ cm2 when a magnetic field was applied. Capacitance measurements (15.16% increase) and ECSA measurements (22.1% increase) also corroborated this. The overpotential measurement decreased from 243.03 mV to 239.1 mV at 100 mA/ cm2. As a result, for both sets of catalysts, the magnetic field improved the current density. Comparatively OER performance in absence of magnetic field of the electrocatalyst which was synthesized by electrodeposition with applied magnetic field was better than (for the second catalyst OER activity studied under applied magnetic field. This suggests that rather than applying a magnetic field during long-term electrolysis, one may opt to apply a magnetic field during electrocatalyst production. When we compared the OER performance of these two, we discovered that NF/Fe-NiCo exhibits the greatest activity of all catalysts at 1.5V, with 91.3 mA/ cm2, although the percentage rise is lower than that of the other catalysts. However, compared to the rise in activity, the ECSA data reveals a significant increment of 56%. The data on capacitance and overpotential likewise correspond with the current density trend. With the lowest overpotential of 236.35 mV when measured at 100 mA/cm2, the NF/NiCo catalyst performed the best overall among all the catalysts. Our findings underscore the significance of electron spin polarization in boosting electrocatalytic performance, offering a promising avenue for the design and development of advanced catalysts for sustainable energy applications and in the context of their commercial viability and integration into industrial-scale electrochemical devices.

Structure–Activity–Stability Relationship of Ru-Ir-Ti Electrocatalysts for the Oxygen Evolution Reaction

Environmentally friendly strategies for energy conversion and storage are urgently needed to account for natural intensity variations of power generation by renewables and to ensure a stable electrical grid. Green hydrogen, produced by water electrolysis, can be considered as one of the most promising energy carriers since it can balance the energy demand in multiple energy sectors. Proton exchange membrane water electrolyzers (PEMWE) are state of the art devices for on-site hydrogen production. Still, their upscaling is challenged by the corrosive acidic environment and sluggish anodic oxygen evolution reaction (OER), which demand using noble metal based catalysts [1, 2]. Currently, Ir-based oxides are employed as OER catalysts in commercial PEMWE as they provide the best balance between activity and stability. Yet, the scarcity and high market price of Ir lead to poor cost-benefit factors. In the last years, Ir-Ru mixed oxides have attracted significant attention of the community due to their improved electrocatalytic activity [2, 3]. However, Ru degradation during the OER becomes challenging in conditions of long-term operation of the electrolyzer. Therefore, balancing stability and activity towards the OER at reduced Ir loading remains a significant challenge in PEMWE.Here, we examine the effect of low additions of Ti (1 to 6 at. %) on the catalytic activity and stability of Ru-Ir alloys towards the OER [4]. The catalysts are synthesized as ternary Ru-Ir-Ti thin film material libraries with Ir contents below 50 at. %. After the high-throughput screening of these libraries for desired electrocatalytic properties by online inductively coupled plasma mass spectrometry (ICP-MS), the most promising alloy compositions are selected and tested in conditions of long-term electrolysis (Figure 1). The observed activity-stability trends are correlated with the electronic structure of the Ru-Ir-Ti catalysts derived from X-ray photoelectron (XPS) and X-ray absorption spectroscopies (XAS). Furthermore, the structural changes in the near-surface regions of these catalysts induced by the OER, are investigated with the aid of atom probe tomography (APT). Our data reveal formation of Ir-Ru hydrous oxide layers in the course of the OER, providing high catalytic activity, while Ti additions promote stabilization of these reactive oxides in the near surface region. Our multidisciplinary approach of combining advanced electrochemical, spectroscopic and atomic-scale characterization methods provides insights on structure-function relationships in electrocatalysis, guiding the rational design of active and stable electrocatalysts.[1.] Carmo, M., et al., A comprehensive review on PEM water electrolysis. International journal of hydrogen energy, 2013. 38(12): p. 4901-4934.[2.] Kasian, O., et al., On the Origin of the Improved Ruthenium Stability in RuO2-IrO2 Mixed Oxides. Journal of the Electrochemical Society, 2016. 163(11): p. F3099-F3104.[3.] Saveleva, V.A., et al., Uncovering the stabilization mechanism in bimetallic ruthenium–iridium anodes for proton exchange membrane electrolyzers. The journal of physical chemistry letters, 2016. 7(16): p. 3240-3245.[4.] Lahn, L., et al. Low Ti Additions to Stabilize Ru‐Ir Electrocatalysts for the Oxygen Evolution Reaction. ChemElectroChem, 2023, e202300399. DOI: https://doi.org/10.1002/celc.202300399. Figure 1

Effect of Light and Electrode Polarization on BiVO4 and TiO2 Photoanodes for Glycerol Oxidation

In recent years, there has been a growing interest in the photoelectrochemical oxidation of glycerol to produce high-value products. Most studies have focused solely on the photocatalytic properties of the electrodes, overlooking their electrocatalytic properties and the different products obtained under dark conditions. Our work aims to address this gap by comparing the electrocatalytic activity under dark and light conditions to determine whether light influences the reactivity of the electrodes or if it just reduces the overpotential of the reaction. To achieve this, we employed two model semiconductors, TiO2 and BiVO4. We have analyzed their polarization curves under both dark and light conditions and evaluated the competence of glycerol oxidation reaction with the oxygen evolution reaction. Furthermore, we conducted long-term (photo)electrolysis revealing the beneficial role of light on the electrolytic process, as it enables the obtention of C3 products on illuminated TiO2 photoanodes at low electrode polarization, comparable to the performance of BiVO4.

Covalent versus noncovalent attachments of [FeFe]‑hydrogenase models onto carbon nanotubes for aqueous hydrogen evolution reaction

In an effort to develop the biomimetic chemistry of [FeFe]‑hydrogenases for catalytic hydrogen evolution reaction (HER) in aqueous environment, we herein report the integrations of diiron dithiolate complexes into carbon nanotubes (CNTs) through three different strategies and compare the electrochemical HER performances of the as-resulted 2Fe2S/CNT hybrids in neutral aqueous medium. That is, three new diiron dithiolate complexes [{(μ-SCH2)2N(C6H4CH2C(O)R)}Fe2(CO)6] (R = N-oxylphthalimide (1), NHCH2pyrene (2), and NHCH2Ph (3)) were prepared and could be further grafted covalently to CNTs via an amide bond (this 2Fe2S/CNT hybrid is labeled as H1) as well as immobilized noncovalently to CNTs via π-π stacking interaction (H2) or via simple physisorption (H3). Meanwhile, the molecular structures of 1–3 are determined by elemental analysis and spectroscopic as well as crystallographic techniques, whereas the structures and morphologies of H1-H3 are characterized by various spectroscopies and scanning electronic microscopy. Further, the electrocatalytic HER activity trend of H1 > H2 ≈ H3 is observed in 0.1 M phosphate buffer solution (pH = 7) through different electrochemical measurements, whereas the degradation processes of H1-H3 lead to their electrocatalytic deactivation in the long-term electrolysis as proposed by post operando analysis. Thus, this work is significant to extend the potential application of carbon electrode materials engineered with diiron molecular complexes as heterogeneous HER electrocatalysts for water splitting to hydrogen.

In-situ exsolution of FeCo nanoparticles over perovskite oxides for efficient electrocatalytic nitrate reduction to ammonia via localized electrons

FeCo nanoparticles exsolved from Co-doped Sm0.9FeO3 nanofibers with abundant oxygen vacancies (Vos) are proposed as an efficient electrocatalyst to promote nitrate reduction reaction (NITRR). Such catalyst achieves a maximum Faradaic efficiency (FE) of 90.3 % and a large NH3 yield of 17.2 mg h−1 mg−1cat. at a negatively shifted potential of −0.9 V in 0.1 M PBS with 0.1 M NaNO3, and the alloy nanoparticles socketed into nanofibers remain extremely stable during long-term electrolysis. The reaction pathway favoring the formation of NH2OH is uncovered by in situ electrochemical tests and theoretical calculations reveal the exsolution of FeCo alloy combined with the generation of Vos enhances nitrate adsorption and lowers energy increase of the potential determining step. Finite-element simulations unveil the applied current and charges are localized on the alloys along the nanofiber, which confirms the exsolved FeCo nanoparticles are the main active sites for NITRR.

Efficient Hydrogen Production over Molybdenum Tungsten Bimetallic Oxide NF/PMonW12-n Catalyst on Nickel Foam.

Developing inexpensive, efficient, and stable catalysts is crucial for reducing the cost of electrolytic hydrogen production. Recently, polyoxometalates (POMs) have gained attention and widespread use due to their excellent electrocatalytic properties. This study designed and synthesized three composite materials, NF/PMonW12-n, by using phosphomolybdic-tungstic heteropolyacids as precursors to grow in situ on nickel foam via the hydrothermal process and subsequent calcination. Then, their catalytic performances are systematically investigated. This work demonstrates that the NF/PMonW12-n catalysts generate more low valent oxides under the synergistic effect of Mo and W, further enhancing activity for hydrogen evolution reaction (HER). Among these electrocatalysts, NF/PMo6W6 exhibits the perfect HER performance, η10 is only 74 mV. It also shows great stability during long-term electrolysis. The current study introduces a fresh approach for producing electrocatalysts that are both cost-effective and highly efficient.

Highly anti-corrosive NiFe LDHs–NiFe alloy hybrid enables long-term stable alkaline seawater electrolysis

Highly anti-corrosive NiFe LDHs–NiFe alloy hybrid enables long-term stable alkaline seawater electrolysis

High-performance bipolar membrane for CO2 electro-reduction to CO in organic electrolyte with NaOH and Cl2 produced as byproducts

Bipolar membranes (BPM) are a special class of ion-exchange membranes constituted by a cation- and an anion-exchange layer, allowing the generation of protons and hydroxide ions via water dissociation. This unique feature makes them useful in a wide range of application. In this work, we have fabricated a novel BPM, with SnO2 hollow spheres used as water dissociation catalyst. Such fabricated BPM has been served as a diaphragm to construct a three-chamber electrolyzer for CO2 electro-reduction to CO in organic electrolyte. During the long-term electrolysis process, the cathodic current density has reached to ∼96.5 mA cm−2, with the Faraday efficiency of CO stabled at ∼92.6 %. Compared with widely used commercial BPM, as-prepared BPM exhibited many advantages, such as lower hydrolysis over-potential, high catalytic efficiency and low total resistance. This technology extends the prospect of BPM application in the field of CO2 reduction.

Electrochemical Analysis of an Electrolyte-Supported Solid Oxide Cell-Based MK35x Stack during Long-Term Electrolysis Operation

The currently ongoing scale-up of high-temperature solid oxide electrolysis (SOEL) requires an understanding of the underlying dominant degradation mechanisms to enable continuous progress in increasing stack durability. In the present study, the degradation behavior of SOEL stacks of the type “MK35x” with chromium-iron-yttrium (CFY) interconnects and electrolyte-supported cells (ESC) developed at Fraunhofer IKTS was investigated. For this purpose, the initial electrochemical performance of a 10-cell stack was characterized in various operating conditions in both fuel cell and electrolysis mode. Degradation was evaluated during galvanostatic steady-state steam electrolysis operation for more than 3000 h at an oxygen side outlet temperature of 816 °C and a current density of −0.6 A cm−2 and showed an average voltage evolution rate of −0.3%/kh demonstrating high stability. Initial and final characterization at the part load operating point at −0.39 A cm−2 and 800 °C led to the determination of a positive overall degradation rate of 0.4%/kh showing a considerable impact of the operating conditions on the degradation rate. By means of electrochemical impedance spectroscopy analysis it was shown that the stack’s ohmic resistance increased whereas the polarization resistance decreased most likely due to an enhancement in LSMM’/ScSZ oxygen electrode performance.

Sulfur poisoned PtNi/C catalysts toward two-electron oxygen reduction reaction for acidic electrosynthesis of hydrogen peroxide

Selective electrocatalysis of two-electron oxygen reduction reaction (2e– ORR) has been recognized as a sustainable and on-site process for hydrogen peroxide (H2O2) production. Great progress has been achieved for 2e– ORR in alkaline media. However, it is challenged by insufficient activity and selectivity of the catalysts in acidic electrolytes. Herein, we report sulfur-poisoned PtNi/C catalysts (PtNiSx/C) that could regulate ORR from the 4e– to 2e– pathway. The identified PtNiS0.6/C offers high activity in terms of onset potential of ∼0.69 V (vs. RHE) and ∼80 % selectivity. The mass activity is also comparable and outperforms representative Pt-based precious and transition-metal-based catalysts. In addition, it is interestingly found that the Faradaic efficiency further increased to 95 % during the long-term electrolysis test due to Ni atom surface migration. The electrochemical production of the H2O2 system was applied to the electro-Fenton process, which has realized the effective degradation of organic pollutants. This work offers a strategy by sulfur poisoning PtNi/C catalyst to realize Pt-based 2e– ORR active catalysts to electrolysis of H2O2 in acidic media.

3D hierarchical porous N-doped carbon nanoarchitecture coated bimetallic phosphides as a highly efficient bifunctional electrocatalyst for overall water splitting

As the energy and ecological crises are increasingly grim, it is challengeable but extremely attractive to fabricate highly efficient and low-cost bifunctional electrocatalysts for overall water splitting (OWS). Herein, a bimetallic phosphide embedded in N-doped hierarchical porous carbon (CoP/Ni2P@NHPC) framework was successfully constructed by calcination and phosphorization of cobalt–nickel coordination polymer nanoflowers (Co/Ni CPNFs), which were obtained by a facile hydrothermal process. Benefitting from their fascinating architecture and composition, the as-prepared CoP/Ni2P@NHPC exhibits outstanding electrochemical properties for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) with small Tafel slopes (103.9 mV dec-1, 62.58 mV dec-1) and ultralow overpotentials (275 mV, 159 mV at 10 mA cm−2) in alkaline medium. Additionally, the CoP/Ni2P@NHPC can be used as a bifunctional catalyst in a two-electrode water splitting device, and it only requires a low cell voltage of 1.55 V to attain the current density of 10 mA cm−2. Meanwhile, the CoP/Ni2P@NHPC also present admirable durability (at least 20 h) under long-term electrolysis. This work gives inspiration for the preparation of highly active bifunctional electrocatalysts for OWS.