Anti–corrosive FeO decorated CuCo2S4 as an efficient and durable electrocatalyst for hydrogen evolution reaction

Nitrogen-Doped CuO@CuS Core-Shell Structure for Highly Efficient Catalytic OER Application

Water electrolysis is a highly efficient route to produce ideally clean H2 fuel with excellent energy conversion efficiency and high gravimetric energy density, without producing carbon traces, unlike steam methane reforming, and it resolves the issues of environmental contamination via replacing the conventional fossil fuel. Particular importance lies in the advancement of highly effective non-precious catalysts for the oxygen evolution reaction (OER). The electrocatalytic activity of an active catalyst mainly depends on the material conductivity, accessible catalytically active sites, and intrinsic OER reaction kinetics, which can be tuned via introducing N heteroatoms in the catalyst structure. Herein, the efficacious nitrogenation of CuS was accomplished, synthesized using a hydrothermal procedure, and characterized for its electrocatalytic activity towards OER. The nitrogen-doped CuO@CuS (N,CuO@CuS) electrocatalyst exhibited superior OER activity compared to pristine CuS (268 and 602 mV), achieving a low overpotential of 240 and 392 mV at a current density of 10 and 100 mA/cm2, respectively, ascribed to the favorable electronic structural modification triggered by nitrogen incorporation. The N,CuO@CuS also exhibits excellent endurance under varied current rates and a static potential response over 25 h with stability measured at 10 and 100 mA/cm2.

rGO functionalized (Ni,Fe)-OH for an efficient trifunctional catalyst in low-cost hydrogen generation via urea decomposition as a proxy anodic reaction

Green hydrogen derived from the water-electrolysis route is emerging as a game changer for achieving global carbon neutrality. Economically producing hydrogen through water electrolysis, however, requires the development of low-cost and highly efficient electrocatalysts via scalable synthetic strategies. Herein, this work reports a simple and scalable immersion synthetic strategy to deposit reduced graphene oxide (rGO) nanosheets integrated with Ni-Fe-based hydroxide nanocatalysts on nickel foam (NF) at room temperature. As a result of synergetic interactions among the hydroxides, rGO and NF, enhanced catalytic sites with improved charge transport between the electrode and electrolyte were perceived, resulting in significantly enhanced oxygen evolution reaction (OER) activity with low overpotentials of 270 and 320 mV at 100 and 500 mA cm^-2, respectively, in a 1.0 M KOH aqueous electrolyte. This performance is superior to those of the hydroxide-based electrode without incorporating rGO and the IrO₂-benchmark electrode. Furthermore, when the conventional OER is substituted with urea decomposition (UOR) as a proxy anodic reaction, the electrolyzer achieves 100 and 500 mA cm^-2 at a lower potential by 150 and 120 mV, respectively than the OER counterpart without influencing the hydrogen evolution reaction (HER) activity at the cathode. Notably, the rGO-incorporated electrode delivers a spectacularly high UOR current density of 1600 mA cm^-2 at 1.53 V vs. RHE, indicating the decomposition of urea at an outstandingly high rate.

Nanostructurally engineered TiO2 embedded Mentha aquatica biowaste derived carbon for supercapacitor applications

The invention of cost-effective, clean, and eco-friendly energy storage technology has been capturing a lot of worldwide interest. Herein, biogenically synthesized TiO₂ nanoparticles (NPs) were ultrasonically coupled with biomass-derived activated carbon (BAC) to obtain composite (denoted as TiO₂@BAC). With the inspiration of nature, Mentha Aquatica leaves extract was employed for biogenic preparation of TiO₂ NPs, and residual solid waste (SW) after extract was subsequently utilized for BAC. It is noteworthy that, this unique intensive method does not require any harmful or toxic chemicals and solvents, and no secondary waste is generated. TEM analysis of TiO₂@BAC revealed spherical morphology of TiO₂ NPs (average size ∼ 18 nm) that were accumulated on nanosheets. Raman, XRD, and XPS manifested the successful construction of TiO₂@BAC. The electrochemical performance of the as-synthesized BAC, TiO₂ NPs, and TiO₂@BAC electrodes was tested towards supercapacitor applications. Notably, the TiO₂@BAC electrode exhibited capacitance of 149 F/g at a current density of 1 A/g, which is approximately twice than that of the bare TiO₂ electrode (76 F/g) along with excellent capacitance restoration of ∼99%. The TiO₂@BAC electrode further revealed outstanding cyclic stability, exhibiting capacitance retention of ∼90% (at 5 A/g) after 10,000 charge/discharge cycles. Furthermore, the TiO₂@BAC electrode delivered optimal specific energy density (6.96 Wh/kg) and large power density (2.07 kW/kg at 10 A/g). Moreover, the TiO₂@BAC delivers an excellent restoration and retention performances of ∼100 and ∼95% (after 10,000 cycles) at 1 A/g with ∼98% coulombic efficiency in symmetric configuration (maximum cell voltage of 1.2 V).

Self-supported efficient hydrogen evolution catalysts with a core-shell structure designed via phase separation

The development of cost-effective, high-performance and flexible electrocatalysts for hydrogen production is of scientific and technological importance. Catalysts with a core-shell structure for water dissociation have been extensively investigated. However, most of them are nanoparticles and thus their catalytic properties are inevitably limited by the use of binders in practice. Herein, this work reports a physical-metallurgy-based structural design strategy to develop a self-supported and unique nanoporous structure with core-shell-like ligaments, i.e., a Cu core surrounded by a NiO shell, formed on a metallic glass (MG) substrate. These newly developed noble metal-free catalysts exhibit outstanding HER performance; the overpotential reaches 67 mV at a current density of 10 mA cm^-2, accompanied by a low Tafel slope of 40 mV dec^-1 and good durability. More importantly, the current strategy could be readily applied to fabricate other nanoporous metals, which opens a new space for designing advanced catalysts as cost-effective electrode materials.