Search

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]

Effective integration of multiple active moieties and strategic engineering of coordinated interfacial junctions are crucial for optimizing the reaction kinetics and intrinsic activities of heterogeneous electrocatalysts. Herein, a simple integrated heterostructure of biphasic Co0.7Fe0.3/Fe3C embedded on in situ grown N‐doped carbon sheets is constructed. Rationally designed CoFe/Fe3C‐T2 owns more accessible active sites and interfacial junction effects, cooperatively boosting the electron and mass transfer, needed for multifunctional electrocatalysis. Leveraging the synergistic effect of dual active sites, CoFe/Fe3C‐T2 demonstrates outstanding oxygen electrocatalytic activity in alkaline medium with an ultra‐low potential gap of 0.58 V, surpassing the recently available state‐of‐the‐art catalysts. Moreover, CoFe/Fe3C‐T2 air‐electrode achieves a high peak power density of 249 mW cm−2, a large specific capacity of 808 mAh g−1 and excellent cycling stability for aqueous Zn‐air batteries. Remarkably, the solid‐state flexible ZAB also exhibits satisfactory performance, showcasing an open‐circuit voltage of 1.43 V and a peak power density of 66 mW cm−2. These outstanding results push this catalyst to the top of the list of non‐noble metal‐based electrode materials. This work offers a viable method for using the active‐site‐uniting strategy to create double‐active‐site catalysts, which may find real‐time applications in energy conversion/storage devices. [ABSTRACT FROM AUTHOR]

The Ostwald process, which is producing HNO3 for commercial use, involves the catalytic oxidation of NH3 and a series of chemical reactions conducted under severe operating conditions. Due to their energy‐intensive nature, these activities play a major role in greenhouse gas emissions and global energy consumption. In response to the urgent requirements of the global energy and environmental sectors, there is an increasingly critical need to develop novel, highly efficient, and environmentally sustainable methods. Herein, CoPc/C3N4 electrocatalyst, integrating CoPc nanotubes with C3N4 nanosheets, is shown. The CoPc/C3N4 electrocatalyst demonstrates yield rate of 871.8 µmol h−1 gcat−1 at 2.2 V, with corresponding Faradaic efficiency (FE) of 46.4% at 2.1 V, which notably surpasses that of CoPc. Through a combination of experimental investigations and density functional theory (DFT) calculations, this study shows that CoPc anchored on C3N4 effectively simplifies the adsorption and activation of chemically inactive nitrogen molecules. The improved catalytic activity for composite system may be the reason of re‐distribution of charges over the CoPc, tuning the valence orbital of Co center due to the presence of 2D layer of C3N4. This mechanism significantly lowers the energy barrier required for critical breaking of inert N2, ultimately leading to a significant improvement in N2 oxidation efficiency. [ABSTRACT FROM AUTHOR]

Electrochemical nitrogen reduction reaction (e-NRR) is an eco-friendly alternative approach to generate ammonia under ambient conditions, with very low power supply. But, developing of an efficient catalyst by suppressing parallel hydrogen evolution reaction as well as avoiding the catalysts poisoning either by hydrogen or electrolyte ion is an open question. So, in order to screen the single atom catalysts (SACs) for the e-NRR, we proposed a descriptor-based approach using density functional theory (DFT) based calculations. We investigated total 24 different SACs of types TM-Pc, TM-N3C1, TM-N2C2, TM-NC3 and TM-N4, considering transition metal (TM). We have considered mainly BF3 ion to understand the role of electrolyte and extended the study for four more electrolyte ions, Cl, ClO4, SO4, OH. Herein, to predict catalytic activity for a given catalyst we have tested 16 different electronic parameters. Out of those, electronic parameter dxz↓ occupancy, identified as electronic descriptor, is showing an excellent linear correlation with catalytic activity (R2 = 0.86). Furthermore, the selectivity of e-NRR over HER is defined by using an energy parameter ∆G*H-∆G*NNH. Further, the electronic descriptor (dxz↓ occupancy) can be used to predict promising catalysts for e-NRR, thus reducing the efforts on designing future single atom catalysts (SACs)., (© 2024 Wiley‐VCH GmbH.)

The increasing demand for clean hydrogen production over fossil fuels necessitates the development of sustainable piezoelectrochemical methods that can overcome the limitations of conventional electrocatalytic and photocatalytic approaches. In this regard, existing piezocatalysts face challenges related to their low piezoelectricity or active site coverage for hydrogen evolution reaction (HER). Driven by global environmental concerns, there is a compelling push to engineer practical materials for highly efficient HER. Herein, monoelemental 2D tellurium (Te) is presented as a class of layered chalcogenide with a non-centrosymmetric crystal structure (P3 1 21 space group). The refined Te nanosheets demonstrate an unprecedented highly efficient H 2 production rate ≈9000 µmol g -1  h -1 under ultrasonic mechanical vibration due to built-in piezo-potential in the system. The remarkable piezocatalytic performance of Te nanosheets arises from a synergistic interplay between their semi-metallic nature, favorable free energy landscape, enhanced electrical conductivity and outstanding piezoelectricity. As a proof of concept, the theoretical approach based on Density Functional Theory (DFT) validates the findings due to the gradual exposure of active sites on the Te nanosheets leading to a self-optimized catalytic performance for hydrogen generation. Therefore, mechanically driven Te emerges as a promising piezocatalyst with the potential to revolutionize highly efficient and sustainable technology for futuristic applications., (© 2024 Wiley‐VCH GmbH.)

Doping is considered a promising material engineering strategy in electrochemical nitrogen reduction reaction (NRR), provided the role of the active site is rightly identified. This work concerns the doping of group VIB metal in Ag 3 PO 4 to enhance the active site density, accompanied by d-p orbital mixing at the active site/N 2 interface. Doping induces compressive strain in the Ag 3 PO 4 lattice and inherently accompanies vacancy generation, the latter is quantified with positron annihilation lifetime studies (PALS). This eventually alters the metal d-electronic states relative to Fermi level and manipulate the active sites for NRR resulting into side-on N 2 adsorption at the interface. The charge density deployment reveals Mo as the most efficient dopant, attaining a minimum NRR overpotential, as confirmed by the detailed kinetic study with the rotating ring disk electrode (RRDE) technique. In fact, the Pt ring of RRDE fails to detect N 2 H 4 , which is formed as a stable intermediate on the electrode surface, as identified from in-situ attenuated total reflectance-infrared (ATR-IR) spectroscopy. This advocates the complete conversion of N 2 to NH 3 on Mo/Ag 3 PO 4 -10 and the so-formed oxygen vacancies formed during doping act as proton scavengers suppressing hydrogen evolution reaction resulting into a Faradaic efficiency of 54.8% for NRR., (© 2024 Wiley‐VCH GmbH.)

C 2 products are more desirable than C 1 products during CO 2 electroreduction (CO 2 ER) because the former possess higher energy density and greater industrial value. For CO 2 ER, Cu is a well-known catalyst, but the selectivity toward C 2 products is still a big challenge for researchers due to complex intermediates, different final products, and large space of the catalyst due to its morphology, plane, size, host surface etc. Using density functional theory (DFT) calculations, we find that alloying of Cu nanoparticles can help to enhance the selectivity toward C 2 products during CO 2 ER with a low overpotential. By a systematic investigation of 111 planes (which prefer the C 1 product in the case of bulk Cu), the alloys show the generation of C 2 products via *CO-*CO dimerization (* indicates adsorbed state). It also suppresses the counter-pathway of hydrogenation of *CO to *CHO, which leads to C 1 products. Further, we find that *CH 2 CHO is the bifurcating intermediate to distinguish between ethanol and ethylene as the final product. We have used simple graphical construction to identify the catalyst for CO 2 ER over HER, and vice versa. We have also defined the case of hydrogen poisoning and projected a parity plot to recognize the catalyst for C 2 product evolution over the C 1 product. Our study reveals that Cu-Ag and Cu-Zn catalysts selectively promote ethanol production on 111 planes. Moreover, an edge-doped 2SO 2 graphene nanoribbon as the host layer further lowers the barrier and selectively promotes ethanol on Cu 38 - and Cu 79 -based alloys. This work provides new theoretical insights into designing Cu-based nanoalloy catalysts for C 2 product formation on the 111 plane.