Ashakiran Maibam

Controlling crystallographic orientation and facet exposure in 2D bismuth oxyhalide materials is critical for numerous applications, including efficient (photo)catalysis and enhanced charge transport. Oriented bismuth oxyhalide thin films are of strategic importance not only for their intrinsic properties but also as a gateway to many other valuable materials via their ability to undergo facile topotactic reactions. To progress the numerous applications linked to this family of materials this work identifies, for the first time, the mechanism regulating crystal orientation in bismuth oxyhalide (BiOI) thin films. Detailed experiments, backed by density functional theory (DFT) calculations, reveal the pivotal role of iodine (halide) anions to modify the van der Waals stacking energies required to direct orientation. Using our methodology, we demonstrate (001) BiOI thin films on commercially relevant wafer scales with unprecedented (001) crystallographic alignment—addressing the key challenge of scalability. To probe structure‐function relations, we fabricate BiOI photodetectors. Compared to unoriented devices, our (001)‐oriented films demonstrate vastly increased operational stability, fewer trap states, ON/OFF signal switching up to 10 ⁵ , low (pA) noise levels, and millisecond response times. Our work can be used as a general methodology to control orientations in BiOX and related chalcohalide systems.

MXenes are known for their remarkable properties, such as high conductivity, hydrophilic surfaces, high densities of active sites, mechanical properties, easy mass transport, unique tunable electronic properties, etc., which have established them as a rising star in the field of 2D materials. In the present study, a Co9S8@Mo2C@Co3O4 heterostructure was synthesized, and its electrocatalytic activity toward the hydrogen evolution reaction (HER) was evaluated. The Co9S8@Mo2C@Co3O4 electrocatalysts exhibited a low overpotential of 103 mV at 10 mA cm−2 and a Tafel slope of 79 mV dec−1, indicating faster HER kinetics in 0.5 M H2SO4. Furthermore, its stability was tested by performing 5000 LSV cycles and chronoamperometry for 24 h, where no significant deviation in its performance was noted. Moreover, this study was also corroborated by performing multistep chronopotentiometry, which proved the long-term operational stability of the electrode under repeated current cycling. The experimental evidence was substantiated by computational studies, which showed that the Co9S8@Mo2C@Co3O4 heterostructure exhibited a closer to optimal hydrogen adsorption free energy (ΔGH*) of −0.18 eV, indicating weaker H* binding that promotes rapid H2 evolution. The superior HER activity is ascribed to an upshifted d-band center (−0.46 eV) and strong interfacial charge transfer from Mo2C to Co9S8 and consequently to electron-enriched Co3O4 in Co9S8@Mo2C@Co3O4 heterostructure. This superior HER performance of the synthesized Co9S8@Mo2C@Co3O4 heterostructure was convincingly established through a synergistic combination of experimental and theoretical insights.

Planarity of graphene supports with point defects and ad-atom vanadium metal single atom catalyst, V-SAC@graphene highlights the structural retainability of the catalyst for industrial applications. First-principles calculations of N2 chemisorption and reduction efficiency on pristine, single vacancy graphene (SVG) and double vacancy graphene shows V-SAC to show a difference in the catalytic activity when changes are introduced onto the coordination of the metal atom and the electronic behaviour of the adsorbates are found to change favourably in case of double vacancy graphene systems. A facile protonation and reduction of N2 to NH3 is observed in DVG catalyst following dπ-pπ* electron transfer from V-metal to N2 gas and subsequent σ-dπ* electron back donation from N2 gas to V-metal. A case of mono-atom doping of boron on double vacancy graphene with V-SAC has been proposed as an efficient NRR catalyst and the NRR limiting potential of -0.36 V and the inclusion of planarity for optimal application of graphene-based has been proposed.

Two-dimensional (2D) metal organic framework (MOF) or metalloporphyrin nanosheets with a stable metal-N₄ complex unit present the metal as a single-atom catalyst dispersed in the 2D porphyrin framework. First-principles calculations on the 3d-transition metals in M-TCPP are investigated in this study for their surface-dependent electronic properties including work function and d-band center. Crystal orbital Hamiltonian population (-pCOHP) analysis highlights a higher contribution of the bonding state in the M-N bond and antibonding state in the N-N bond to be essential for N-N bond activation. A linear relationship between ΔG_max and surface electronic properties, N-N bond strength, and Bader charge has been found to influence the rate-determining potential for nitrogen reduction reaction (NRR) in M-TCPP MOFs. 2D Ti-TCPP MOF, with a kinetic energy barrier of 1.43 eV in the final protonation step of enzymatic NRR, shows exclusive NRR selectivity over competing hydrogen reduction (HER) and nitrogenous compounds (NO and NO₂). Thus, Ti-TCPP MOF with an NRR limiting potential of -0.35 V in water solvent is proposed as an attractive candidate for electrocatalytic NRR.

Visible-light-active alkyl group-wrapped unsymmetrical squaraine dyes SD1-SD3 were synthesized, featuring an indoline donor and pyridine and carboxylic acid anchoring groups. Their photophysical, electrochemical, and photovoltaic characteristics were examined by fabricating a dye-sensitized solar cell (DSSC) device. Both carboxylic acid and pyridine anchoring groups containing squaraine dyes SD3 and SD2 possess similar photophysical and electrochemical characteristics. However, their photovoltaic performances were completely different. The SD3 dye with the carboxylic acid anchoring group displayed a DSSC device efficiency of 7.20% (V-OC 0.81 V; J(SC) 12.29 mA/cm(2)) using iodolyte (I-/I-3(-)) electrolyte, compared to SD1 (V-OC 0.659 V; J(SC) 4.97 mA/cm(2); and eta - 2.34%) and SD2 (V-OC 0.629 V; J(SC) 1.68 mA/cm(2); and eta - 0.84%), which were featured with pyridyl anchoring groups. These results were attributed to dye loading on the Lewis and Br & oslash;nsted acidic sites of TiO2 and the importance of aggregated structures for photocurrent generation. In the incident photon-to-current efficiency (IPCE) analysis, SD1 dye-sensitized devices exhibited photocurrent generation from both monomeric and aggregated dyes on the TiO2 surface. In contrast, SD2 showed photocurrent generation solely from aggregated states. Despite the introduction of long alkyl chains to reduce dye aggregation and charge recombination, the results indicated preferential charge injection from only the aggregated SD2 dye on TiO2. Fluorescence-quenching experiments indicated an efficient charge transfer from the aggregated SD2 dye to TiO2 compared to that of the monomeric dye. Cosensitization, a method to enhance the light-harvesting efficiency and photocurrent generation in DSSCs, was explored by simultaneously cosensitizing pyridyl-based dyes (SD1 and SD2) with a blue-colored carboxylic acid-based squaraine dye SD4. IPCE analysis demonstrated that both SD1 and SD4 contributed to generating a photocurrent of 9.11 mA/cm(2). The sequential cosensitization of SD1 and SD4 with the coadsorbent CDCA showed the highest performance, with a V-OC of 0.663 V, a J(SC) of 11.43 mA/cm(2), and an efficiency (eta) of 5.20%.

Introducing complementary active materials in tandem as heterostructures of various shapes and sizes can significantly improve the physicochemical properties of the developed materials. Recently, the use of amorphous materials in conjunction with crystalline moieties as highly efficient electrocatalysts for water-splitting electrolyzers has surged rapidly. Excellent bifunctional activity for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) can be achieved from amorphous–crystalline-based materials owing to their remarkably conductive crystalline phase as well as their long-range disordered amorphous phase. In addition, the high specific surface area, disordered structure, and enhanced structural stability can accommodate various defects and strains that develop during in situ electrochemical reactions. Consequently, amorphous materials can be used as both surface-confined and volume-confined electrocatalysts. Although crystalline materials have better electronic properties as well as higher thermal and mechanical stability, they suffer from limited activity due to only surface-confined electrocatalysis. In this regard, the judicious integration of crystalline and amorphous active materials suitable for the OER and HER can tremendously enhance their bifunctional electrocatalytic activities owing to their synergistic effects. The variety in the choice of amorphous and crystalline counterparts presents ample opportunities for further exploration of the development of amorphous–crystalline heterostructured materials with unique properties. However, considering the recent massive developments in the understanding and protocols for fabricating such heterostructures, a critical review is vital for further advancement in this direction. Although some review papers have focused only on amorphous materials, including their synthesis methods, properties, and applications, no critical review that provides an overview emphasizing amorphous–crystalline heterostructures for electrocatalytic water-splitting applications has been published. In this regard, this review aims to present comprehensive details on the recent developments in the fabrication of different amorphous–crystalline heterostructures, the choice of the composition of each component, and the resulting physicochemical properties for the OER, HER, and overall water-splitting. It provides an in-depth understanding of amorphous–crystalline material synthesis protocols, their selection rationale, and their targeted physicochemical properties. This review also provides thought-provoking ideas and long-term perspectives for future research.

A series of alkyl-group-wrapped and halogen atom functionalized unsymmetrical squaraine dyes (ISQ) were designed and synthesized. A maximum DSSC device efficiency of 7.80% was achieved for iodine funtionalized ISQ-I dye in Z-150 with CDCA.

Perovskite solar cells (PSCs) emerged as potential photovoltaic energy-generating devices developing in recent years because of their excellent photovoltaic properties and ease of processing. However, PSCs are still reporting efficiencies much lower than their theoretical limits owing to various losses caused by the charge transport layer and the perovskite. In this regard, herein, an interface engineering strategy using functional molecules and chemical bridges was applied to reduce the loss of the heterojunction electron transport layer. As a functional interface layer, ethylenediaminetetraacetic acid (EDTA) was introduced between PCBM and the ZnO layer, and as a result, EDTA simultaneously formed chemical bonds with PCBM and ZnO to serve as a chemical bridge connecting the two. DFT and chemical analyses revealed that EDTA can act as a chemical bridge between PCBM and ZnO, passivate defect sites, and improve charge transfer. Optoelectrical analysis proved that EDTA chemical bridge-mediated charge transfer (CBM-CT) provides more efficient interfacial charge transport by reducing trap-assisted recombination losses at ETL interfaces, thereby improving device performance. The PSC with EDTA chemical bridge-mediated heterojunction ETL exhibited a high PCE of 21.21%, almost no hysteresis, and excellent stability to both air and light.