Exploring the role of iron in Fe_(5)Ni_(4)S_(8)toward oxygen evolution through modulation of electronic orbital occupancy

Ni-Fe-based catalysts are considered to be among the most active catalysts for the oxygen evolution reaction(OER)under alkaline conditions,with Fe playing a crucial role.However,Fe leaching occurs during the reaction due to thermodynamic instability,which has resulted in conflicting reports within the literature regarding its role.To clarify this point,we propose a strategy consisting of modulating the electronic orbital occupancy to suppress the extensive loss of Fe atoms during the OER process.Theoretical calculations,in-situ X-ray photoelectron spectroscopy,molecular dynamics simulations,and a series of characterization showed that the stable presence of Fe not only accelerates the electron transfer process but also optimizes the reaction barriers of the oxygen evolution intermediates,promoting the phase transition of Fe_(5)Ni_(4)S_(8)to highly active catalytic species.The modulated Fe_(5)Ni_(4)S_(8)-based pre-catalysts exhibit improved OER activity and long-term durability.This study provides a novel perspective for understanding the role of Fe in the OER process.

Mn incorporated RuO_(2) nanocrystals as an efficient and stable bifunctional electrocatalyst for oxygen evolution reaction and hydrogen evolution reaction in acid and alkaline

The development of efficient and stable bifunctional overall water-splitting is a crucial goal for clean and renewable energy,which is a challenging task.Herein,we report an Mn-incorporated RuO_(2)(MnRuO_(2))catalyst for highly efficient electrocatalytic oxygen evolution reaction(OER)and hydrogen evolution reaction(HER)in acid and alkaline media.Benefiting from a more electrochemical active area with the incorporation of Mn,the Mn-RuO_(2)required an overpotential of 200 mV to attain a current density of 10 mA/cm^(2)for OER in acid.DFT result indicates that the doping of Mn into RuO_(2)can enhance the OER activity.An acidic overall water-splitting electrolyzer with good stability constructed by bifunctional Mn-RuO_(2)only requires a cell voltage of 1.50 V to afford 10 m A/cm^(2)and can operate stably for 50 h at50 mA/cm^(2),which is better than the state-of-the-art Ru-based catalyst.Additionally,the Mn-Ru O_(2)exhibits excellent HER and OER activity in alkaline media,and it shows superior activity and durability for overall water-splitting,only needing a cell voltage of 1.49 V to attain 10 m A/cm^(2).The present work provides an efficient approach to designing and constructing efficient Ru-based electrocatalysts for overall water-splitting.

Metal-free porous nitrogen-doped carbon nanotubes for enhanced oxygen reduction and evolution reactions

Developing efficient metal-free bi-functional electrocatalysts is required to reduce costs and improve the slow oxygen reduction reaction （ORR） and oxygen evo- lution reaction （OER） kinetics in electrochemical systems. Porous N-doped carbon nanotubes （NCNTs） were fabri- cated by KOH activation and pyrolysis of polypyrrole nanotubes. The NCNTs possessed a large surface area of more than 1,000 m2 g-1. NCNT electrocatalysts, particu- larly those annealed at 900 ℃, exhibited excellent ORR electrocatalytic performance. Specifically, they yielded a more positive onset potential, higher current density, and long-term operation stability in alkaline media, when compared with a commercially available 20 wt% Pt/C catalyst. This resulted from the synergetic effect between the dominant pyridinic/graphitic-N species and the porous tube structures. The NCNT electrocatalyst also exhibited good performance for the OER. The metal-free porous nitrogen-doped carbon nanomaterials were prepared from low cost and environmentally friendly precursors. They are potential alternatives to Pt/C catalysts, for electrochemical energy conversion and storage.

Ir-Pd nanoalloys with enhanced surface-microstructure-sensitive catalytic activity for oxygen evolution reaction in acidic and alkaline media

Ir-based dectrocatalysts have been system- atically studied for a variety of applications, among which the electrocatalysis for oxygen evolution reaction （OER） is one of the most prominent. The investigation on surface-micro- structure-sensitive catalytic activity in different pH media is of great significance for developing efficient electrocatalysts and corresponding mechanism research. Herein, shape-tunable Ir- Pd alloy nanocrystals, including nano-hollow-spheres （NHSs）, nanowires （NWs）, and nanotetrahedrons （NTs）, are synthe- sized via a facile one-pot solvothermal method, Electro- chemical studies show that the OER activity of the Ir-Pd alloy nanocatalysts exhibits surface-microstructure-sensitive en- hancement in acidic and alkaline media. Ir-Pd NWs and NTs show more than five times higher mass activity than com- mercial Ir/C catalyst at an overpotential of 0.25 V in acidic and alkaline media. Post-XPS analyses reveal that surface Ir（VI） oxide generated at surface defective sites of Ir-Pd nanocata- lysts is a possible key intermediate for OER. In acidic medium, the specific activity of Ir-Pd nanocatalysts has a positive cor- relation with the surface roughness of NWs 〉 NHSs 〉 NTs. However, the strong dissociation of surface Ir（VI） species （IrO42-） at surface defective sites is a possible obstacle for the formation of Ir（VI） oxide, which reverses the activity sequence for OER in alkaline medium.

Three-dimensional interconnected Ni（Fe）OxHy nanosheets on stainless steel mesh as a robust integrated oxygen evolution electrode

The development of an electrocatalyst based on abundant elements for the oxygen evolution reaction （OER） is important for water splitting associated with renewable energy sources. In this study, we develop an interconnected Ni（Fe）OxHy nanosheet array on a stainless steel mesh （SSNNi） as an integrated OER electrode, without using any polymer binder. Benefiting from the well- defined three-dimensional （3D） architecture with highly exposed surface area, intimate contact between the active species and conductive substrate improved electron and mass transport capacity, facilitated electrolyte penetration, and improved mechanical stability. The SSNNi electrode also has excellent OER performance, including low overpotential, a small Tafel slope, and long-term durability in the alkaline electrolyte, making it one of the most promising OER electrodes developed.