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A hybrid material comprising nickel hydroxide (Ni(OH)2) enveloped in a poly(ionic liquid) (PIL-Br), poly(1-butyl-3-vinylimidazolium bromide), is effectively employed as an additive in this study, wherein PIL-Br provides precise control over the shape and arrangement of Ni(OH)2 crystals. The PIL can chemically couple with the as-synthesized Ni(OH)2, imparting a modified surface electronic structure. This innovation introduces a fresh perspective for energy storage applications. Extensive characterization, along with density functional theory calculations, has explored the impact of PIL polymer groups. The findings indicate that these polymers facilitate a more favourable redox response on the surface of Ni(OH)2. The desired morphology of the nanoarchitectonics leads to a high performing solid-state free-standing device with 245 F g−1 specific capacitance at 1 A g−1. When integrated with an activated carbon electrode and a unique polyvinyl 1-butyl-3-methylimidazolium tetrafluoroborate/polyvinyl alcohol (BMIMBF4/PVA) configuration, the hybrid device achieves an ED of 86.2 W h kg−1 at a PD of 800 W kg−1. Profoundly, it retains a capacity retention of 96% even after undergoing 10 000 cycles at 5 A g−1. The utilization of stabilized nanoarchitectonics incorporating redox-active polymers marks a novel direction in various energy applications. [ABSTRACT FROM AUTHOR]

Descriptors are properties or parameters of a material that are used to explain any catalytic activity both computationally and experimentally. Such descriptors aid in designing the material's properties to obtain an efficient catalyst. For transition metals, the d-band center is a well-known descriptor that shows a Sabatier type relationship for several catalytic reactions. However, it fails to explain the activity when considering the same metal active site with a varying local environment. To address this, density functional theory was used for single atom catalysts (SACs) embedded on armchair and zigzag graphene nanoribbons (AGNR and ZGNR). By varying the anchoring nitrogen atoms' orientation and considering pristine and doped cases, 432 active sites were used to test the oxygen evolution reaction (OER) activity. It was observed that S and SO2 dopants help in reducing the overpotential on Co-SAC (η = 0.28 V). Along with the d-band center, a total of 105 possible descriptors were individually tested and failed to correlate with the OER activity. Furthermore, PCA was employed to narrow down unique descriptors, and machine learning algorithms (MLR, RR, SVR, RFR, BRR, LASSO, KNN and XGR) were trained on the two obtained descriptors. Among the models, SVR and RFR models showed the highest performances with R2 = 0.89 and 0.88 on test data. This work shows the necessity for a multi-descriptor approach to explain OER catalytic activity on SACs and the approach would help in identifying similar descriptors for other catalytic reactions as well. [ABSTRACT FROM AUTHOR]

The electrochemical reduction of nitrate to ammonia (NO3RR) catalyzed by metal organic frameworks (MOFs) is a promising and efficient method for reducing nitrate pollution in water while simultaneously producing a valuable product, ammonia. Herein, we report the 3D nanoarray architecture of the metal organic complex Fe-(tetracyanoquinodimethane)2 Fe(TCNQ)2 as an efficient electrocatalyst that exhibits a high ammonia yield rate of 11 351.6 μg h−1 cm−2 and faradaic efficiency (FE) of 85.2% at −1.1 V vs. RHE and excellent catalytic stability up to 2 days. The excellent catalytic performance is evaluated by ATR-FTIR spectroscopy and a series of control experiments. Density functional-based theoretical calculations are carried out to identify Fe–N4 active sites in metal–organic network structures. This study showcases the advancement of transition metal-based organic frameworks as very effective electrocatalysts for the reduction of nitrate to ammonia (NH3). [ABSTRACT FROM AUTHOR]

The oxygen reduction reaction (ORR) is largely influenced by material conductivity as well as electron transfer mobility. Usually, covalent porous polymers are fascinating in terms of the surface area and availability of abundant functionalities serving as active sites. However, this class of materials largely suffers from electronic conductivity issues, which limits their extensive application in electrocatalytic reactions. To overcome this long-standing issue, herein, we have developed a metallo [Fe(II)]-porphyrin-pyrene based pi-conjugated porous polymer (FePP), which was further modified with electrophoretically exfoliated graphene (FePP@G30/3/7). The interfacing of these two units via π–π interaction introduces the flexibility of >C–C< bond rotation resulting in-plane flipping of the bridging –Ph ring from out of plane orientation. The ring flipping-induced co-planarity was investigated through experimental and computational studies. In situ FTIR and operando Raman studies reveal that the ORR process with the FePP@G30/3/7 catalyst follows a 4e− reduction pathway. This phenomenon drives axial as well as equatorial charge mobility within the system influencing the active FeN4 site toward lowering the overpotential for the ORR. [ABSTRACT FROM AUTHOR]

Utilization of bifunctional high-efficiency non-precious electrocatalysts for stable and effective water splitting is crucial to the growth of the clean energy industry. Topologically, the predetermined ordered structures of metal–organic frameworks (MOFs) can be contrived through the judicious assembly of a tailor-made synthesis strategy of layered double hydroxide (LDH) films. Aiming at NiCo-LDH@NH2-UiO-66 as a model system, for the first time, we examine the 2-methyl imidazole-induced ultrathin 2D NiCo-LDH nanosheet arrays in NH2-UiO-66 as an effective bifunctional electrocatalytic system for overall H2O splitting with marvellous performance and robustness in alkaline environments. The progressively tuned NiCo-LDH@NH2-UiO-66 catalyst demands overpotential values of 296 and 224 mV to deliver a current density of 50 mA cm−2 for the O2 evolution reaction (OER) and H2 evolution reaction (HER) in 1 M KOH aqueous solution, respectively. Tafel studies also revealed favorable reaction kinetics during electrochemical processes. The NiCo-LDH@NH2-UiO-66 bifunctional electrode displayed superior activity exhibiting a voltage of 1.65 V at a benchmarking current density of 10 mA cm−2 towards overall water splitting. Importantly, the NiCo-LDH@NH2-UiO-66 electrode shows an excellent specific capacitance of 0.00364 mF cm−2 with remarkable durability of the capacitor after 1000 cycles. To compare with the experimental result, we have performed density functional theory (DFT)-based calculation to estimate the HER and OER activity of the NiCo-LDH@NH2-UiO-66 heterostructure. From the HER free energy profile and Bader charge analysis, we have confirmed that the presence of NH2-UiO-66 helps in H2 production with 0.10 eV free energy of H2 adsorption (GH*). From the OER free energy profile, the estimated overpotential (η) is about 0.96 eV, which confirms that the electrochemical reaction towards the OER is also possible on the NiCo-LDH@NH2-UiO-66 structure. This study will bestow a beneficial blueprint for the utilization of an effective, durable, and economical MOF-based bifunctional catalytic system for overall water splitting. [ABSTRACT FROM AUTHOR]

Layered two-dimensional (2D) materials demonstrate exceptional performance as supercapacitor electrodes due to their unique intrinsic properties. A hybrid 2D/2D heterostructured electrode material can synergize the individual energy storage features of each of the layered 2D materials. Ti3C2 MXene is an emergent 2D material with enriched energy storage capabilities but suffers from certain vulnerabilities during the charge storage process. Vanadium ditelluride (VTe2) is an interesting yet unexplored layered material within the 2D transition metal dichalcogenide (TMD) family. Owing to the unique structural features, VTe2 showcases certain advantages in energy storage. The formation of the VTe2/Ti3C2 MXene heterostructure for energy storage applications has not been reported until now. Herein, we report a facile and simple hydrothermal synthesis approach to prepare bare VTe2 and the VTe2/MXene heterostructure for supercapacitor applications. The energy storage mechanism in the heterostructure is systematically analyzed. The synergistically induced interplaying effects enhance the specific capacitance of the heterostructure to 250 F g−1 along with excellent durability during long cycle operation. Consequently, an asymmetric system is constructed with VTe2/MXene as the positive electrode and MoS2/MXene as the negative electrode. The 2D/2D heterostructure-based asymmetric supercapacitor delivers excellent performance with an energy density of 46.3 W h kg−1 and a highest power density of 6400 W kg−1. Furthermore, the density functional theory calculations predict that the enhancement of electronic Te 5P states near the Fermi level due to MXene leads to improved performance of the VTe2/Ti3C2 hybrid for supercapacitor applications. [ABSTRACT FROM AUTHOR]

Using a first principles approach, we investigated the catalytic activity of a noble metal-free n-doped (C → B, O → N) hexagonal boron nitride (h-BN) monolayer for CO oxidation. The CO adsorption ability and hence the preferred Eiley -- Rideal (ER) and Langmuir-Hinshelwood (LH) mechanism for CO oxidation is dopant-dependent: CO is chemisorbed on O-doped h-BN (OBN) while it physically interacts with the C-doped h-BN (CBN) surface. Even though both C and O doping create similar donor states below the Fermi level (E[sub f]), O doping results in a larger bond length of O-B1 (one of the nearest B atom), out-of-plane displacement of the B1 atom, and less positive charge on the B1 atom, synergistically contributing to higher atomic activity. The presence of a pre-adsorbed O[sub 2] molecule on both types of surfaces eliminates any chances of CO poisoning of the surface, and CO oxidation prefers to proceed via the ER mechanism with a small activation barrier. The high values of Sabatier activities suggest that the doped h-BN surface is superior to Au55 and Pt55 nanoclusters. In case of CO oxidation by means of the LH mechanism, a stable O2…CO intermediate is produced, which requires a high barrier energy to break the O-O bond. However, the presence of a H2O molecule increases the activity of the catalyst and helps in catalytic CO de-poisoning. [ABSTRACT FROM AUTHOR]