Bimetallic ZIF-Derived Co/N-Codoped Porous Carbon Supported Ruthenium Catalysts for Highly Efficient Hydrogen Evolution Reaction

Unveiling the Dual Active Sites of Ni/Co(OH)2-Ru Heterointerface for Robust Electrocatalytic Alkaline Seawater Splitting

Constructing bifunctional electrocatalysts through the synergistic effect of diverse metal sites is crucial for achieving high-efficiency and steady overall water splitting. Herein, a "dual-HER/OER-sites-in-one" strategy is proposed to regulate dominant active sites, wherein Ni/Co(OH)2-Ru heterogeneous catalysts formed on nickel foam (NF) demonstrate remarkable catalytic activity for oxygen evolution reaction (OER) as well as hydrogen evolution reaction (HER). Meanwhile, the potentials@10 mA cm-2 of Ni/Co(OH)2-Ru@NF for overall alkaline water and seawater splitting are only 1.36 and 1.41 V, respectively, surpassing those of commercial RuO2@NF and Pt/C@NF. The Ru site is identified as the primary active site for HER by density functional theory (DFT) calculations, while the Co(OH)2 site displays the minimal rate-determining step energy barrier (RDS) and functions as the main active site for OER. This study offers novel perspectives on the rational utilization of diverse metal species' catalytic capabilities for developing dual active sites multifunctional electrocatalysts.

Engineering the Sandwich-Type Porphyrinic MOF-Ruthenium-Nickel Foam Electrode for Boosting Overall Water Splitting via Self-Reconstruction

The rational construction of a hierarchical noble metal-metal-organic frameworks (MOFs) structure is anticipated to yield enduring and highly efficient performance in alkaline electrocatalytic water splitting. Herein, a sandwich construction strategy is employed to enhance the stability, wherein active RutheniRu (Ru) nanosheets are incorporated onto nickel foam (NF) and subsequently covered with porphyrinic MOFs (PMOFs). In addition, activated PMOF-NiOOH-Ru20/NF-C/A electrodes are obtained by electrochemical self-reconstruction as cathode and anode, respectively. Density functional theory (DFT) calculations demonstrated that the resulting PMOF-NiOOH-Ru heterointerface effectively facilitated electron transfer, enhanced H2O adsorption capacity, and optimized ΔG values for *H and *O to *OOH. Consequently, PMOF-NiOOH-Ru20/NF-C/A exhibited low overpotentials for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), accompanied by minimal Ru leakage. Furthermore, stable overall water splitting can be achieved with a low voltage of 1.456 V@10 mA cm-2 for over 120 h. Even when operated in simulated seawater, the prepared electrodes demonstrated similar activity and stability. This study contributes to a deeper understanding of the regulation mechanism for the performance and stability of active sites in the electrocatalytic self-reconstruction process.

Revealing the Role of Ruthenium on the Performance of P2-Type Na0.67Mn1-xRuxO2 Cathodes for Na-Ion Full-Cells

Herein, P2-type layered manganese and ruthenium oxide is synthesized as an outstanding intercalation cathode material for high-energy density Na-ion batteries (NIBs). P2-type sodium deficient transition metal oxide structure, Na0.67Mn1-xRuxO2 cathodes where x varied between 0.05 and 0.5 are fabricated. The partially substituted main phase where x = 0.4 exhibits the best electrochemical performance with a discharge capacity of ≈170 mAh g-1. The in situ X-ray Absorption Spectroscopy (XAS) and time-resolved X-ray Diffraction (TR-XRD) measurements are performed to elucidate the neighborhood of the local structure and lattice parameters during cycling. X-ray photoelectron spectroscopy (XPS) revealed the oxygen-rich structure when Ru is introduced. Density of States (DOS) calculations revealed the Fermi-Level bandgap increases when Ru is doped, which enhances the electronic conductivity of the cathode. Furthermore, magnetization calculations revealed the presence of stronger Ru─O bonds and the stabilizing effect of Ru-doping on MnO6 octahedra. The results of Time-of-flight secondary-ion mass spectroscopy (TOF-SIMS) revealed that the Ru-doped sample has more sodium and oxygenated-based species on the surface, while the inner layers mainly contain Ru-O and Mn-O species. The full cell study demonstrated the outstanding capacity retention where the cell maintained 70% of its initial capacity at 1 C-rate after 500 cycles.

Lotus-biowaste derived sulfur/nitrogen-codoped porous carbon as an eco-friendly electrocatalyst for clean energy harvesting

Recent research is focused on biomass-derived porous carbon materials for energy harvesting (hydrogen evolution reaction) because of their cost-effective synthesis, enriched with heteroatoms, lightweight, and stable properties. Here, the synthesis of porous carbon (PC) materials from lotus seedpod (LP) and lotus stem (LS) is reported by the pyrolysis method. The porous and graphitic structure of the prepared LP-PC and LS-PC materials were confirmed by field emission scanning electron microscopy, transmission electron microscopy with selected area electron diffraction, X-ray diffraction, and nitrogen adsorption-desorption measurements. Heteroatoms in LP-PC and LS-PC materials were investigated by attenuated total reflection-Fourier transform infrared and X-ray photoelectron spectroscopy. The specific surface area of LP-PC and LS-PC were calculated as 457 and 313 m² g^-1, respectively. Nitrogen and sulfur enriched LP-PC and LS-PC materials were found to be effective electrocatalysts for hydrogen evolution reactions. LP-PC catalyst showed a very low overpotential of 111 mV with the Tafel slope of 69 mV dec^-1, and LS-PC catalyst achieved a Tafel slope of 85 mV dec^-1 with a low overpotential of 135 mV. This work is expected to be extended for the development of biomass as a sustainable porous carbon electrocatalyst with a tunable structure, elements, and electronic properties. Furthermore, preparing carbon materials from the biowaste and applying clean energy harvesting might reduce environmental pollution.

Photocatalytic and Electrocatalytic Properties of Cu-Loaded ZIF-67-Derivatized Bean Sprout-Like Co-TiO2/Ti Nanostructures

ZIF-derivatized catalysts have shown high potential in catalysis. Herein, bean sprout-like Co-TiO2/Ti nanostructures were first synthesized by thermal treatment at 800 °C under Ar-flow conditions using sacrificial ZIF-67 templated on Ti sheets. It was observed that ZIF-67 on Ti sheets started to thermally decompose at around 350 °C and was converted to the cubic phase Co3O4. The head of the bean sprout structure was observed to be Co3O4, while the stem showed a crystal structure of rutile TiO2 grown from the metallic Ti support. Cu sputter-deposited Co-TiO2/Ti nanostructures were also prepared for photocatalytic and electrocatalytic CO2 reduction performances, as well as electrochemical oxygen reaction (OER). Gas chromatography results after photocatalytic CO2 reduction showed that CH3OH, CO and CH4 were produced as major products with the highest MeOH selectivity of 64% and minor C2 compounds of C2H2, C2H4 and C2H6. For electrocatalytic CO2 reduction, CO, CH4 and C2H4 were meaningfully detected, but H2 was dominantly produced. The amounts were observed to be dependent on the Cu deposition amount. Electrochemical OER performances in 0.1 M KOH electrolyte exhibited onset overpotentials of 330-430 mV (vs. RHE) and Tafel slopes of 117-134 mV/dec that were dependent on Cu-loading thickness. The present unique results provide useful information for synthesis of bean sprout-like Co-TiO2/Ti hybrid nanostructures and their applications to CO2 reduction and electrochemical water splitting in energy and environmental fields.