Yingfang Yao

In Situ Fabrication of Highly Conductive Metal Nanowire Networks with High Transmittance from Deep-Ultraviolet to Near-Infrared

We have developed a facile and compatible method to in situ fabricate uniform metal nanowire networks on substrates. The as-fabricated metal nanowire networks show low sheet resistance and high transmittance (2.2 Ω sq(-1) at T = 91.1%), which is equivalent to that of the state-of-the-art metal nanowire networks. We demonstrated that the transmittance of the metal networks becomes homogeneous from deep-ultraviolet (200 nm) to near-infrared (2000 nm) when the size of the wire spacing increases to micrometer size. Theoretical and experimental analyses indicated that we can improve the conductivity of the metal networks as well as keep their transmittance by increasing the thickness of the metal films. We also carried out durability tests to demonstrate our as-fabricated metal networks having good flexibility and strong adhesion.

Highly Functional Bioinspired Fe/N/C Oxygen Reduction Reaction Catalysts: Structure-Regulating Oxygen Sorption

Tuna is one of the most rapid and distant swimmers. Its unique gill structure with the porous lamellae promotes fast oxygen exchange that guarantees tunas high metabolic and athletic demands. Inspired by this specific structure, we designed and fabricated microporous graphene nanoplatelets (GNPs)-based Fe/N/C electrocatalysts for oxygen reduction reaction (ORR). Careful control of GNP structure leads to the increment of microporosity, which influences the O2 adsorption positively and desorption oppositely, resulting in enhanced O2 diffusion, while experiencing reduced ORR kinetics. Working in the cathode of proton-exchange membrane fuel cells, the GNP catalysts require a compromise between adsorption/desorption for effective O2 exchange, and as a result, appropriate microporosity is needed. In this work, the highest power density, 521 mW·cm(-2), at zero back pressure is achieved.

Rapid synthesis of nitrogen-doped graphene by microwave heating for oxygen reduction reactions in alkaline electrolyte

Abstract Nitrogen-doped graphene (NG) with a nitrogen content from 4.05 wt% to 5.47 wt% was rapidly prepared via microwave heating of graphene under NH 3 flow. The as-synthesized NG samples were then used as electrocatalysts in the oxygen reduction reaction (ORR) in alkaline solution. The NG samples showed excellent ORR catalytic activity with an onset potential of 0.17 V, which is comparable to that of commercial Pt/C electrocatalyst (0.21 V). The structure, composition, and nitrogen species of the NG samples were examined by transmission electron microscopy, Raman spectroscopy, elemental analysis and X-ray photoelectron spectroscopy. The onset potential increases with the content of graphite nitrogen in the NG samples, indicating that graphite nitrogen might be the main factor controlling the performance of the NG samples in the ORR. The results showed that NG prepared by rapid microwave heating is a promising ORR catalyst for fuel cells.

Vitamin E assisted polymer electrolyte fuel cells

Due to breathing O2 from the air, vertebrates can suffer from diseases originating from oxidative stress. These, however, can be relieved by various antioxidants. Similarly, proton exchange membrane fuel cells (PEMFCs) suffer from the major problem of limited lifetimes, caused by chemical attacks by reactive oxygen species (ROS). Inspired by vertebrates, we herein show that the incorporation of a natural antioxidant, α-tocopherol (α-TOH), the most abundant component of vitamin E, which acts as a free radical scavenger, enables a maintenance of performance for PEMFCs which is impossible to achieve for fuel cells in the absence of α-TOH. It is notable that oxidized α-TOH can in turn be reduced by permeated H2 during fuel cell operation, resulting in its regeneration. Such reversibility leads to a chemical circulation system, which not only ensures the effective recycling of α-TOH, but also permits efficient protection of proton exchange membranes (PEMs) and thus allows their long-term operation.

Adjusting the Crystallinity of Mesoporous Spinel CoGa2O4 for Efficient Water Oxidation

Effective and stable electrocatalysts (ECs) are of great importance for the modification of semiconductor (SC) photoanodes, to achieve efficient photoelectrochemical (PEC) water splitting. Herein we demonstrate that the low-crystallinity mesoporous spinel CoGa2O4 oxygen evolution catalyst (OEC), exhibiting excellent bulk electrocatalytic stability and activity for oxygen-evolving reaction (OER), obviously improved water oxidization on a-Fe2O3 photoanode. Low crystallinity not only balances the stability and activity for ECs themselves but facilitates formation of adjustable Schottky junctions between ECs and SCs. Those would contribute to surface state passivation and photogenerated hole extraction, leading to lower onset potential and larger photocurrent. Thus, our finding suggests that low crystallinity could serve as a beneficial feature of ECs to achieve efficient PEC water splitting, owing to its preponderant tendency for the improvement of interface reaction kinetics.

One-dimensional assembly of TiO2 nanoparticles toward enhancing light harvesting and electron transport for application in dye-sensitized solar cells

One-dimensional (1D) assembly of TiO2 nanoparticles (NPs) was successfully achieved by an improved electrospinning technique. Electrospinning precursor solution was prepared with conventional TiO2 NPs and polyvinylpyrrolidone dispersed in ethanol. The newly developed 1D assembly of nanoparticles (AS-NP) has been introduced into the photoanode in dye-sensitized solar cells (DSSCs). Compared to the traditional disordered stacking of TiO2 NPs, the AS-NPs bring in faster charge transport and longer electron lifetime, as well as a higher light scattering ability (especially in the wavelength range from 500 nm to 650 nm). It is exhibited that the AS-NPs can enhance electron transport and light scattering, while retaining the merits of NP morphology. Consequently, the efficiency of a cell based on an AS-NP/NP bilayer photoanode could be improved by about 15% in comparison to a reference cell made of absolute TiO2 NPs.

Investigation of the durability of a poly- p -phenylenediamine/carbon black composite for the oxygen reduction reaction

Nitrogen-doped carbon materials exhibiting high oxygen reduction reaction activity were prepared via the pyrolysis of a poly- p -phenylenediamine/carbon black composite. The as-synthesized catalyst showed excellent catalytic activity in alkaline solution, and outperformed commercial Pt/C in KOH solution (0.1 mol/L), as demonstrated by the higher current density and the more positive half-wave potential. Scanning electron microscopy and N 2 adsorption-desorption analyses indicated that a composite structure, in which the N-rich surface of the poly- p -phenylenediamine had an increased active center concentration and the high external surface area of the carbon black was conducive to the mass transport, is highly beneficial in terms of promoting the oxygen reduction reaction. However, the activity of this catalyst underwent an obvious decrease following exposure to air for 30 d. X-ray photoelectron spectroscopy showed that the oxygen content in the catalyst was increased by prolonged air exposure. O 1 s spectrum showed increases in the C=O and C-O components, suggesting that atmospheric oxygen reacted with the catalyst. This oxidation leaded to the deactivation of active center, thus the catalytic activity decreased. Based on these results, the stability in air of nitrogen-doped carbon materials must be taken into consideration when assessing applications as alternatives to platinum-based materials.

Unlocking the potential of graphene for water oxidation using an orbital hybridization strategy

Graphene-based electrocatalytic materials are potential low-cost electrocatalysts for the oxygen evolution reaction (OER). However, substantial overpotentials above thermodynamic requirements limit their efficiency and stability in OER-related energy conversion and storage technologies. Here, we embedded CrN crystals into graphene and in situ electrochemically oxidized them to construct graphene materials with encapsulated Cr6+ ions (Cr6+@G). These Cr6+@G materials exhibit the lowest OER overpotential of 197 mV at 10 mA cm−2 and excellent stability over 200 h at a high current density of about 120 mA cm−2 in an alkaline electrolyte. Spectroscopic and computational studies confirm a stable ion coordination environment significantly benefiting the downshift of the graphene Fermi level via hybridization of C p orbitals with d orbitals of Cr6+ ions that enhances the OER activity and stability.

Highly Durable and Active Ternary Pt-Au-Ni Electrocatalyst for Oxygen Reduction Reaction

Long‐term stable and high active catalysts for oxygen reduction reaction (ORR) are required for the commercialization of proton exchange membrane fuel cells (PEMFCs). Platinum (Pt) catalyst is the preferred choose for ORR, but the stability and activity of existing Pt catalyst are unsatisfactory for the commercialization of PEMFCs. Here the ternary Pt–Au–Ni/C and binary Pt–Ni/C are synthesized by a rapid microwave‐assisted polyol reduction. The Pt–Au–Ni/C exhibits superior ORR activity to both of Pt–Ni/C and commercial Pt/C. Moreover, the Pt–Au–Ni/C exhibited the long‐term stability in both of half‐cell and single‐cell accelerated degradation tests. The above results indicate that the addition of Au into binary Pt–Ni catalyst can not only enhance the stability but also improve the electrocatalytic activity.

One-pot synthesis of triazine-framework derived catalysts with high performance for polymer electrolyte membrane fuel cells

The prohibitive cost and scarcity of the precious metals used for oxygen reduction reaction (ORR) catalysts limit the large-scale commercialization of proton exchange membrane fuel cells (PEMFCs). Great efforts have been made to improve the ORR activity of non-precious metal catalysts. Herein, we describe a one-pot synthesis process of preparing triazine-polymer–Fe–C catalysts using polyimide (PI), ferric chloride and melamine as the precursors with a pronounced electrocatalytic activity towards ORR in acid media. The ORR activity of catalysts and the performance of single cells strongly depend on the properties of the carbon supports, which affect the surface areas and microporosities of the final catalysts. The optimized PI–Fe–C catalyst exhibits an excellent performance (onset potential of 0.92 V and the half-wave potential 0.78 V) towards ORR activity in acid medium. A maximum power density of 310 mW cm−2 is obtained with a loading of 2 mg cm−2 in a single cell.