Electrocatalytic activity of electrodeposited CoOx thin film on low-carbon unalloyed steel substrate toward electrochemical oxygen evolution reaction (OER)

Highly Dispersive Metal Atoms Anchored on Carbon Matrix Obtained by Direct Rapid Pyrolysis of Metal Complexes

High current density reaching 1 A cm−2 for efficient oxygen evolution reaction (OER) was demonstrated by interactively optimizing electrolyte and electrode at non‐extreme pH levels. Careful electrolyte assessment revealed that the state‐of‐the‐art nickel‐iron oxide electrocatalyst in alkaline solution maintained its high OER performance with a small Tafel slope in K‐carbonate solution at pH 10.5 at 353 K. The OER performance was improved when Cu or Au was introduced into the FeOx‐modified nanostructured Ni electrode as the third element during the preparation of electrode by electrodeposition. The resultant OER achieved 1 A cm−2 at 1.53 V vs. reversible hydrogen electrode (RHE) stably for 90 h, comparable to those in extreme alkaline conditions. Constant Tafel slopes, apparent activation energy, and the same signatures from operando X‐ray absorption spectroscopy among these samples suggested that this improvement seems solely correlated with enhanced electrochemical surface area caused by adding the third element.

Engineering S, N-doped carbon nanosheets derived from thiazolothiazole-based conjugated polymer for efficient electrocatalytic oxygen evolution and Zn-air battery

A core-shell structured catalyst for enhanced oxygen evolution: NiFe double hydroxide coating over phosphorus -modified NiMoO4 nanorod cores

Stable porous manganese oxide-based electrodes are essential for clean energy generation and storage because of their high natural abundance and health safety. This investigation focuses on mesoporous LiMn2-xMxO4 (where M is Fe, Co, Ni, and Cu and x is 0, 0.1, 0.3, 0.5, and 0.67) electrodes and thin/thick films. The mesoporous electrodes and films are fabricated by coating clear and homogeneous ethanol solutions of the salts (LiNO3, [Mn(OH2)4](NO3)2, and [M(OH2)x](NO3)2) and surfactants (P123 and CTAB) and calcining at elevated temperature (denoted as F-LiMn2-xMxO4, G-LiMn2-xMxO4, and meso-LiMn2-xMxO4, respectively). The electrochemical properties, stability, and oxygen evolution reaction (OER) performance of the F/G-LiMn2-xMxO4 electrodes are investigated in alkaline media using a three electrode setup. The F-LiMn1.33M0.67O4 electrodes (where M is Mn, Fe, Co, and Ni) exhibit low Tafel slopes of 60, 43, 44, and 32 mV/dec, respectively. While all the Mn-rich and F-LiMn2-xFexO4 electrodes degrade via Mn(VI) disproportionation reaction, the 33% Co electrode shows high stability during the OER. The nickel-based electrodes are stable with as little as 15% Ni and display excellent OER performance over 25% Ni, albeit undergoing a transformation that accumulates Ni(OH)2 species on the electrode surface. Copper in the F-LiMn2-xCuxO4 electrodes is homogeneous at low Cu percentages but forms a CuO phase above 15% Cu, undergoes degradation, and displays a weak OER performance. In short, Co and Ni stabilize the F-LiMn1.33Co0.67O4 and F-LiMn1.7Ni0.3O4 electrodes, which display excellent OER performance.

Proton exchange membrane water electrolysis (PEMWE) offers a promising route for the production of green hydrogen from renewable energy sources and could be the master key to unlocking a future sustainable energy system (1). One of the main barriers delaying the wide-spread adoption of PEMWE technologies is the slow kinetics of the oxygen evolution reaction (OER) occurring at the anode and the need for high-cost, low-abundance precious metal electrocatalysts. Iridium-based oxides are still considered the only feasible option for practical applications due to their high activity and considerable corrosion stability under the harsh electrochemical reaction conditions. To improve the overall efficiency of PEMWEs, future electrocatalyst development strategies must concomitantly address performance metrics in terms of activity, stability and material cost.Towards enhancing iridium utilisation, efforts are aimed at increasing the electrochemical surface area of the catalyst per mass of iridium, thereby increasing the number of available electrocatalytic surface sites. In this regard, amorphous iridium oxide (IrOx) nanoparticles have been shown to achieve a high intrinsic activity (2). However, this comes at the expense of catalyst stability (3) and a loss of intrinsic electronic conductivity (4) associated with the lower degree of crystallinity. By maximising the dispersion of Ir-based nanoparticles, the use of high surface area support materials have also been shown to improve OER performance (5, 6).However, to address long-term stability concerns for Ir-based OER catalysts, highly crystalline rutile iridium dioxide (IrO2) materials may still offer the best prospects. The drawback of using this approach is that the formation of crystalline IrO2 nanoparticles often involves high temperature thermal oxidative treatment causing particle growth and loss of surface area, ultimately leading to decreased OER activities (7). Therefore, novel synthesis methods that retain a high degree of crystallinity without a loss of surface area for IrO2 nanoparticles are required.In this talk, we discuss two synthesis strategies geared towards the preparation of highly crystalline IrO2 nanoparticles with high OER performance. Firstly, we present a novel wet-chemistry synthesis method that avoids the use of reducing agents and eliminates the need for high temperature thermal oxidative treatment. The resultant nano-sized IrO2 nanoparticles were found to have excellent Ir mass-specific OER activity and durability attributed to the small nanoparticle size and high degree of crystallinity.Secondly, we present a novel metalorganic chemical deposition process as a simple, one-step preparation method for highly crystalline IrO2 nanoparticles supported on Sb-doped tin oxide (ATO) (8). The superior OER performance was attributed to the epitaxial anchoring of well dispersed, crystalline IrO2 nanoparticles onto the ATO support. We further discuss the versatility of the method to the application of other conductive oxide support materials such as indium tin oxide and F-doped tin oxide, with the ability of tuning the chemical state of the Ir-based nanoparticles by changing the reaction conditions, i.e., temperature and gas environment as well as the nature of the support.Finally, using a series detailed physico-chemical characterisation techniques to elucidate the nature the iridium phase, composition, morphology and structure, we relate these properties to the electrochemical activity and stability of the prepared materials for the OER. Herein, we highlight some of the challenges often encountered with the analysis of physical and electrochemical characterisation data for IrO2 nanoparticles, particularly when supported on other oxide materials. Acknowledgements This work is funded by the Department of Science and Innovation (DSI, South Africa) Impala Platinum Holdings Limited (Implats) and the Federal Minister of Education and Research (BMBF, Germany). References K. Ayers, Current Opinion in Electrochemistry, 18, 9 (2019). T. Reier, I. Weidinger, P. Hildebrandt, R. Kraehnert and P. Strasser, ECS Transactions, 58, 39 (2013). T. Binninger, R. Mohamed, K. Waltar, E. Fabbri, P. Levecque, R. Kötz and T. J. Schmidt, Scientific Reports, 5, 12167 (2015). M. Bernt, C. Schramm, J. Schröter, C. Gebauer, J. Byrknes, C. Eickes and H. A. Gasteiger, Journal of The Electrochemical Society, 168, 084513 (2021). H.-S. Oh, H. N. Nong, T. Reier, A. Bergmann, M. Gliech, J. Ferreira de Araújo, E. Willinger, R. Schlögl, D. Teschner and P. Strasser, Journal of the American Chemical Society, 138, 12552 (2016). A. Hartig-Weiss, M. Miller, H. Beyer, A. Schmitt, A. Siebel, A. T. S. Freiberg, H. A. Gasteiger and H. A. El-Sayed, ACS Applied Nano Materials, 3, 2185 (2020). J. Quinson, Advances in Colloid and Interface Science, 303, 102643 (2022). Z. S. H. S. Rajan, T. Binninger, P. J. Kooyman, D. Susac and R. Mohamed, Catalysis Science & Technology, 10, 3938 (2020).

High performance oxygen reduction and evolution reactions by graphitization of nickel –cobalt framework system

Rapid screening of NixFe1−x/Fe2O3/Ni(OH)2 complexes with excellent oxygen evolution reaction activity and durability by a two-step electrodeposition method

The layered transition metal oxyhydroxides have received increasing interest owing to the efficient energy conversion performance and material stability during oxygen evolution reaction (OER). In particular, Fe-doped Ni oxyhydroxides (NiOOH) have shown the record-high OER performance in alkaline media among various catalysts. Theoretically, under-coordinated facets including Ni4+, exposed at the edges of NiOOH, were predicted to perform highly active OER. Therefore, here we suggest a rational catalyst design that exposes NiOOH edges with Fe-doping, which could improve dramatically the OER performance. This unique structure was successfully prepared by electro-anodization process of Fe‑doped Ni octahedral nanocrystals. After anodization, metallic surface of the nanocrystal was transformed to vertically aligned β‑Fe/NiOOH layers with exposed Ni4+ edge sites. Electrochemical OER and anion exchange membrane based single-cell tests recorded the overpotential of 210 mV at a current density of 10 mA cm−2GEO and stable operation for 5 days, respectively. In-situ/operando studies revealed that the cycle of Ni oxidation state between +2 and +4 assisted by Fe dopant is the key engine that greatly accelerates OER kinetics, and that the aligned β‑Fe/NiOOH layers on Ni octahedra are stable under harsh OER conditions.

Construction of Co/Co2N0.67 nanoparticles embedded S and N-doped carbon from a cobalt-complex as a bifunctional Electrocatalyst for ORR and OER.

Oxygen evolution reaction (OER) is a key step in many energy conversion and storage processes. Here, by rationally adding an appropriate amount of Mn into the lattice of a layered NaxCoO2 parent oxide, high solubility of iron into the NaxCoO2 oxide lattice is realized without the use of an extremely air-sensitive Na2O2 raw material, and the synergy created between the Co and Fe can boost the catalytic activity of the layered oxide for OER. Moreover, the water intercalation capability of the layered oxides can be utilized to make the oxide resemble mixed metal hydroxides, which will also bring a beneficial effect for OER. As a result, the as-developed Na0.67Mn0.5Co0.3Fe0.2O2 (CF-32) layered oxide with an optimal Co/Fe ratio and water intercalation shows high OER performance in alkaline media, overperforming the benchmark IrO2 catalyst. In 0.1 M KOH solution, the novel catalyst shows 0.39 V overpotential at 10 mA cm-2 and favorable stability. The excellent OER performance of CF-32 is due to the synergistic effect of transition-metal elements (Co and Fe) and water intercalation, leading to little charge transfer resistance, large amounts of exposed catalytic active sites, plenty of surface high oxidation state O22-/O- oxygen species, and hydroxide-rich surface. The facile synthesis and high OER performance of CF-32 enriches the non-noble metal family of OER catalysts and boosts the practical application of non-noble metal catalysts.

MOFs derived FeNi3 nanoparticles decorated hollow N-doped carbon rod for high-performance oxygen evolution reaction

Because of the sluggish oxygen evolution kinetics, it is extremely important but still challenging to develop low-cost, efficient, and stable electrocatalysts for oxygen evolution reaction (OER) to enhance the efficiency of water electrolysis. Herein, for the first time, we present a novel heterostructure catalyst, constructed by ultrafine NiS/Fe3O4 heterostructural nanoparticles decorated on a carbon nanotube (CNT) matrix (NiS/Fe3O4 HNPs@CNT), which is synthesized by a facile hydrothermal reaction and subsequent sulfurization process. The NiS/Fe3O4 HNPs@CNT hybrid delivers superior OER activity in alkaline medium: it delivers a current density of 10 mA cm-2 at an ultralow overpotential of 243 mV with a small Tafel slope of 44.2 mV dec-1, which outperforms the benchmark RuO2 electrocatalyst; moreover, it exhibits terrific long-term stability over 36 h without any noticeable performance decay. The exceptional OER performance can be attributed to the unique nanoarchitecture, high conductivity of the CNT matrix, and particularly, the interaction between the Ni and Fe species in NiS/Fe3O4 heterostructural nanoparticles. This work introduces a sensible nanoarchitecture design with a facile and novel fabrication strategy to attain nonprecious metal-based composite catalysts with high OER performance and outstanding long-term stability.

Hierarchy and delithiation regulations on mesoporous LiCoO2 nanosheets for boosted water oxidation electrocatalysis

Seawater electrolysis is expected to play an important role in the circular economy by reducing the hydrogen production cost due to the simplified process lines[1] and by saving scarce sources of safe and fresh water.[2] Seawater impurities especially chloride ions can cause the corrosion of the catalyst and be oxidized at high potential, competing with the oxygen evolution reaction (OER). Produced chlorine and hypochlorite are toxic to humans and the environment,[3] thus selective OER is desirable. Furthermore, impurity cations, such as Ca and Mg, may form hydroxide precipitates in a highly alkaline condition which is commonly used in the commercial electrolyzer. Therefore, selective OER in non-extreme pH (pH < 10) is highly desired, which requires additional challenges on the electrocatalyst and the electrolyte. In this study, we have effectively utilized the thermodynamic potential gap between chloride oxidation reaction (COR) and OER, and engineering of non-noble metal hydroxide electrocatalysts and buffer electrolyte successfully achieved the selective OER in the presence of chloride ion at commercially relevant operation conditions in non-extreme pH within the thermodynamic window.Firstly, the stability of non-noble metal materials in 1.0 mol kg− 1 potassium borate (K-borate, pH 9.2) buffer solution with 0.5 mol kg− 1 KCl was investigated. Ni foam and Ni hydroxide, which are commonly used in water splitting at extreme pH levels, were unstable, and Co, Fe, and Ti-based materials were found to be the candidates for seawater splitting. Among various combinations of these elements, the CoFeOxHy/TF (Ti felt) electrode showed better performance than CoOxHy/TF and FeOxHy/TF electrodes. The CoFeOxHy electrode possessed a three-hold larger double layer capacitance (C dl) which is the electrochemically active surface area than its counterparts. Our kinetic study revealed that Tafel slopes and apparent activation energies of CoFeOxHy resembled the control CoOxHy and FeOxHy electrodes, indicating that the performance difference was originated from the enlarged surface area caused by mixed Co and Fe.In addition to the development of electrocatalysts, electrolyte engineering plays a key role. By employing the CoFeOxHy/TF electrode, the OER performance was investigated in varied molality and counter cation borate electrolytes at pH 9.2. The molarity of K-borate above 1.0 mol kg− 1 was found to be essential to minimize the concentration overpotential, which helps to maintain the electrode potential below the thermodynamic window of COR. The OER performance was insensitive to cation identity except for the Na cation counterpart having a low solubility product. Furthermore, Cl−-containing electrolyte had a higher conductivity than that without Cl−, which can be an advantage to decrease the ohmic resistance in two electrode configurations for future application.The influence of the potential window on the stability and selectivity was investigated by using the developed electrode and 1.0 mol kg−1 K-borate (pH 9.2) with 0.5 mol kg−1 KCl. Below the redox potential of ClO− formation at 1.72 VRHE (V vs. Reversible hydrogen electrode), current density-potential relationships were insensitive to the Cl−. At 1.72 VRHE in the presence of Cl−, the faradaic efficiency (FE) of O2 (FEO2) reached 98±1%, whereas the FE of hypochlorite (FEHC) was merely 1±1%. Above this threshold potential, under chronopotentiometry (CP) testing at 50 mA cm−2 corresponding to approximately 1.82 VRHE, FEO2 decreased to 93±2% and FEHC increased to 7±2%. Critically, the potential of 1.82 VRHE was larger than 1.78 VRHE observed without Cl−, likely due to the blockage of the OER active site by Cl− or related species. Finally, aiming for the practical application, the OER performance over CoFeOxHy was examined at 353 K. The FEO2 reached 99±2% at 500 mA cm− 2 and 1.67 VRHE (Figure 1). Our calculations on thermodynamics revealed that the redox potential of OER decreases to 1.18 VRHE while that of ClO− formation reaction is 1.71 VRHE at 353 K, leaving a potential gap of 530 mV. High selectivity toward the OER was attributed to the consequence of fine engineering of electrocatalysts and electrolytes that successfully maintained the potential below the 1.71 VRHE where the OER is thermodynamically dominant. In addition, the electrode was stable for multiple on-off accelerated stability testing for 10 h at 500 mA cm− 2 and 353 K.Reference[1] S. Dresp, F. Dionigi, M. Klingenhof, P. Strasser, ACS Energy Lett. 2019, 4, 933–942.[2] C. J. Vörösmarty, P. B. McIntyre, M. O. Gessner, D. Dudgeon, A. Prusevich, P. Green, S. Glidden, S. E. Bunn, C. A. Sullivan, C. R. Liermann, Nature 2010, 467, 555–561.[3] J. G. Vos, M. T. M. Koper, J. Electroanal. Chem. 2018, 819, 260–268. Figure 1