Siti Nur Farhana Mohd Nasir

Bio: Siti Nur Farhana Mohd Nasir is an academic researcher from National University of Malaysia. The author has contributed to research in topics: Water splitting & Heterojunction. The author has an hindex of 7, co-authored 15 publications receiving 202 citations.

New Insights into Se/BiVO4 Heterostructure for Photoelectrochemical Water Splitting: A Combined Experimental and DFT Study

Abstract: Monoclinic clinobisvanite BiVO4 is one of the most promising materials in the field of solar water splitting due to its band gap and suitable valence band maximum (VBM) position. We have carried out comprehensive experimental and periodic density functional theory (DFT) simulations of BiVO4 heterojunction with selenium (Se-BiVO4), to understand the nature of the heterojunction. We have also investigated the contribution of Se to higher performance by effecting morphology, light absorption, and charge transfer properties in heterojunction. Electronic properties simulations of BiVO4 show that its VBM and conduction band minimum (CBM) are comprised of O 2p and V 3d orbitals, respectively. The Se/BiVO4 heterojunction has boosted the photocurrent density by 3-fold from 0.7 to 2.2 mA cm–2 at 1.3 V vs SCE. The electrochemical impedance and Mott–Schottky analysis result in favorable charge transfer characteristics, which account for the higher performance in Se/BiVO4 as compared to the BiVO4 and Se. Finally, spec...

High-humidity processed perovskite solar cells

Abstract: Perovskite solar cells (PSCs) are considered the next-in-line technology in the solar industry. This technology can reduce the cost of solar energy to an unprecedented level given their remarkably high efficiency and ease of manufacturing. Hitherto, many studies have preferred well-regulated inert conditions or a low-humidity atmosphere (relative humidity < 30%) for fabricating highly efficient PSCs to avoid the adverse impact of humidity on a perovskite film. This is because humidity is the main reason for perovskite instability and can alter the film growth kinetics during the fabrication process, thereby ultimately affecting the morphology of the grown film and the device performance. The requirement for an inert or low-humidity environment can increase the capital costs of setting up the fabrication facilities and hamper the large-scale production of PSCs. Therefore, efforts have been devoted to preparing PSC devices in a high-humidity environment to comprehend perovskite crystal growth kinetics and improve the morphological properties and stability of the perovskite film. This review highlights the modifications implemented towards (1) perovskite materials, (2) charge-selective layers, and (3) deposition protocols by spin-coating, to adapt a high-humidity atmosphere (RH ≥ 30%) for developing efficient PSCs. The progress of scalable processing methods such as blade-coating, inkjet printing, slot-die coating, and spray-coating, and the translation of spin-coating-modified protocols into these methods are also discussed. Finally, this review provides the remaining challenges to realizing the high-humidity fabrication of PSCs for commercialization.

Rapid fabrication of oxygen defective α-Fe2O3(110) for enhanced photoelectrochemical activities

Abstract: Defect engineering is increasingly recognized as a viable strategy for boosting the performance of photoelectrochemical (PEC) water splitting using metal oxide-based photoelectrodes. However, previously developed methods for generating point defects associated with oxygen vacancies are rather time-consuming. Herein, high density oxygen deficient α-Fe2O3 with the dominant (110) crystal plane is developed in a very short timescale of 10 minutes by employing aerosol-assisted chemical vapor deposition and pure nitrogen as a gas carrier. The oxygen-defective film exhibits almost 8 times higher photocurrent density compared to a hematite photoanode with a low concentration of oxygen vacancies which is prepared in purified air. The existence of oxygen vacancies improves light absorption ability, accelerates charge transport in the bulk of films, and promotes charge separation at the electrolyte/semiconductor interface. DFT simulations verify that oxygen-defective hematite has a narrow bandgap, electron–hole trapped centre, and strong adsorption energy of water molecules compared to pristine hematite. This strategy might bring PEC technology another step further towards large-scale fabrication for future commercialization.

Nanostructure-assisted charge transfer in α-Fe2O3/g-C3N4 heterojunctions for efficient and highly stable photoelectrochemical water splitting.

Abstract: The development of semiconductor heterojunctions is a promising and yet challenging strategy to boost the performance in photoelectrochemical (PEC) water splitting. This paper describes the fabrication of a heterojunction photoanode by coupling α-Fe2O3 and g-C3N4via aerosol-assisted chemical vapour deposition (AACVD) followed by spin coating and air annealing. Enhanced PEC performance and stability are observed for the α-Fe2O3/g-C3N4 heterojunction photoanode in comparison to pristine α-Fe2O3 and the reason is systematically discussed in this paper. Most importantly, the fabricated α-Fe2O3/g-C3N4 film shows impressive stability, retaining more than 90% of the initial current over 12 h operating time. The excellent stability of the heterojunction photoanode is achieved due to the unique nanoflake structure of α-Fe2O3 induced by AACVD. This nanostructure promotes good adhesion with the g-C3N4 particles, as the particles tend to be trapped within the α-Fe2O3 valleys and eventually create strong and large interfacial contacts. This leads to improved separation of charge carriers at the α-Fe2O3/g-C3N4 interface and suppression of charge recombination in the photoanode, which are confirmed by the transient decay time, charge transfer efficiency and electrochemical impedance analysis. Our findings demonstrate the importance of nanostructure engineering for developing heterojunction structures with efficient charge transfer dynamics.

Mn3O4-Graphene Hybrid as a High Capacity Anode Material for Lithium Ion Batteries

Abstract: We developed two-step solution-phase reactions to form hybrid materials of Mn3O4 nanoparticles on reduced graphene oxide (RGO) sheets for lithium ion battery applications. Mn3O4 nanoparticles grown selectively on RGO sheets over free particle growth in solution allowed for the electrically insulating Mn3O4 nanoparticles wired up to a current collector through the underlying conducting graphene network. The Mn3O4 nanoparticles formed on RGO show a high specific capacity up to ~900mAh/g near its theoretical capacity with good rate capability and cycling stability, owing to the intimate interactions between the graphene substrates and the Mn3O4 nanoparticles grown atop. The Mn3O4/RGO hybrid could be a promising candidate material for high-capacity, low-cost, and environmentally friendly anode for lithium ion batteries. Our growth-on-graphene approach should offer a new technique for design and synthesis of battery electrodes based on highly insulating materials.

High Rates of Oxygen Reduction over a Vapor

Abstract: The air electrode, which reduces oxygen (O2), is a critical component in energy generation and storage applications such as fuel cells and metal/air batteries. The highest current densities are achieved with platinum (Pt), but in addition to its cost and scarcity, Pt particles in composite electrodes tend to be inactivated by contact with carbon monoxide (CO) or by agglomeration. We describe an air electrode based on a porous material coated with poly(3,4-ethylenedioxythiophene) (PEDOT), which acts as an O2 reduction catalyst. Continuous operation for 1500 hours was demonstrated without material degradation or deterioration in performance. O2 conversion rates were comparable with those of Pt-catalyzed electrodes of the same geometry, and the electrode was not sensitive to CO. Operation was demonstrated as an air electrode and as a dissolved O2 electrode in aqueous solution.

Review on nanoscale Bi-based photocatalysts

Abstract: Nanoscale Bi-based photocatalysts are promising candidates for visible-light-driven photocatalytic environmental remediation and energy conversion. However, the performance of bulk bismuthal semiconductors is unsatisfactory. Increasing efforts have been focused on enhancing the performance of this photocatalyst family. Many studies have reported on component adjustment, morphology control, heterojunction construction, and surface modification. Herein, recent topics in these fields, including doping, changing stoichiometry, solid solutions, ultrathin nanosheets, hierarchical and hollow architectures, conventional heterojunctions, direct Z-scheme junctions, and surface modification of conductive materials and semiconductors, are reviewed. The progress in the enhancement mechanism involving light absorption, band structure tailoring, and separation and utilization of excited carriers, is also introduced. The challenges and tendencies in the studies of nanoscale Bi-based photocatalysts are discussed and summarized.

Enhanced photoelectrochemical performance of Z-scheme g-C3N4/BiVO4 photocatalyst

Abstract: BiVO4 is a considerably promising semiconductor for photoelectrochemical water splitting due to its stability, low cost and moderate band gap. In this research, g-C3N4 was proposed in Z-scheme configuration which boosted the performance of BiVO4 up to four times. The experimental observations were counterchecked with Density Functional Theory (DFT) simulations. A TiO2/BiVO4 heterojunction was developed and its performance was compared with that of g-C3N4/BiVO4. The photocurrent for g-C3N4/BiVO4 was 0.42 mAcm−2 at 1.23 V vs. RHE which was the highest among g-C3N4 based Z-scheme heterojunction devices. Lower charge transfer resistance, higher light absorption and more oxygen vacancy sites were observed for the g-C3N4 based heterojunction. The simulated results attested that g-C3N4 and BiVO4 formed a van der Waals type heterojunction, where an internal electric field facilitated the separation of electron/hole pair at g-C3N4/BiVO4 interface which further restrained the carrier recombination. Both the valence and conduction band edge positions of g-C3N4 and BiVO4 changed with the Fermi energy level. The resulted heterojunction had small effective masses of electrons (0.01 me) and holes (0.10 me) with ideal band edge positions where both CBM and VBM were well above and below the redox potential of water.

Enhancing photoelectrochemical water splitting by combining work function tuning and heterojunction engineering.

Abstract: We herein demonstrate the unusual effectiveness of two strategies in combination to enhance photoelectrochemical water splitting. First, the work function adjustment via molybdenum (Mo) doping significantly reduces the interfacial energy loss and increases the open-circuit photovoltage of bismuth vanadate (BiVO4) photoelectrochemical cells. Second, the creation and optimization of the heterojunction of boron (B) doping carbon nitride (C3N4) and Mo doping BiVO4 to enforce directional charge transfer, accomplished by work function adjustment via B doping for C3N4, substantially boost the charge separation of photo-generated electron-hole pairs at the B-C3N4 and Mo-BiVO4 interface. The synergy between the above efforts have significantly reduced the onset potential, and enhanced charge separation and optical properties of the BiVO4-based photoanode, culminating in achieving a record applied bias photon-to-current efficiency of 2.67% at 0.54 V vs. the reversible hydrogen electrode. This work sheds light on designing and fabricating the semiconductor structures for the next-generation photoelectrodes. While photoelectrodes represent a promising solar-to-fuel conversion technology, material challenges limit performances. Here, authors improve the onset potential and charge separation of bismuth vanadate photoanode water splitting performances by work function tuning and heterojunction engineering.