Kuei-Hsien Chen

Abstract The present investigation mainly addresses the open circuit voltage (Voc) issue in kesterites based Cu2ZnSn(S,Se)4 solar cells by simply introducing alkali metal fluoride nanolayers (  several nm NaF, or LiF) to lower the work functions of the front İTO\} contacts without conventional hole-blocking ZnO layers. Kelvin probe measurements confirmed that the work function of the front İTO\} decreases from 4.82 to 3.39 and 3.65 eV for NaF and LiF, respectively, resulting in beneficial band alignment for electron collection and/or hole blocking on top electrodes. Moreover, a 10.4% power conversion efficiency ( 11.5% in the cell effective area) \{CZTSSe\} cell with improved Voc of up to 90 mV has been attained. This demonstration may provide a new direction of further boosting the performance of copper chalcogenide based solar cells as well.

The present investigation mainly addresses the open circuit voltage (Voc) issue in kesterite based Cu2ZnSn(S,Se)4 solar cells by simply introducing alkali metal fluoride nanolayers (~ several nm NaF, or LiF) to lower the work functions of the front ITO contacts without conventional hole-blocking ZnO layers. Kelvin probe measurements confirmed that the work function of the front ITO decreases from 4.82 to 3.39 and 3.65 eV for NaF and LiF, respectively, resulting in beneficial band alignment for electron collection and/or hole blocking on top electrodes. Moreover, a 10.4% power conversion efficiency (~ 11.5% in the cell effective area) CZTSSe cell with improved Voc of up to 90 mV has been attained. This demonstration may provide a new direction of further boosting the performance of copper chalcogenide based solar cells as well.

Lithium metal anodes form a dendritic structure after cycling which causes an internal short circuit in flammable electrolytes and results in battery fires. Today's separators are insufficient for suppressing the formation of lithium dendrites. Herein, we report on the use of mesoporous silica thin films (MSTFs) with perpendicular nanochannels (pore size ∼5 nm) stacking on an anodic aluminum oxide (AAO) membrane as the MSTF⊥AAO separator for advancing Li metal batteries. The nanoporous MSTF⊥AAO separator with novel inorganic structures shows ultra-long term stability of Li plating/stripping in Li–Li cells at an ultra-high current density and capacity (10 mA cm−2 and 5 mA h cm−2). A significant improvement over the state-of-the-art separator is evaluated based on three performance indicators, e.g. cycle life, current density and capacity. In Li–Cu cells, the MSTF⊥AAO separator shows a coulombic efficiency of >99.9% at a current density of 10 mA cm−2 for more than 250 h of cycling. The separator gives improved rate capability in Li–LiFePO4 (LFP) batteries. The excellent performance of the MSTF⊥AAO separator is due to good wetting of electrolytes, straight nanopores with negative charges, uniform Li deposition and blocking the finest dendrite.

Polyethersulfone ionomers containing quaternary ammoniums were prepared for the applications on alkaline anion exchange membrane (AAEM) fuel cells. The ionomers were synthesized from 2,2′-dimethyl-4,4′-biphenyldiol and bis(4-chlorophenyl) sulfone via nucleophilic substitution followed by bromination, quaternization and anion exchange reaction. The biphenyl structure in polymer main chain exhibited atropisomerism after bromination, leading to the anisochronous signals of geminal protons on bromomethyl groups in 1H NMR spectra. Model compounds were synthesized to confirm the atropisomerism by EI mass and 1H NMR spectra. The resonance peaks from five possible repeating units of brominated polyethersulfones in the 1H NMR spectra were identified and discussed in detail. The rotational barriers of biphenyl structures containing brominated methyl groups at 2 and 2′ positions were calculated by density functional theory. The properties of these polyethersulfone anion exchange membranes (AEMs) were characterized. Their IECs ranged from 0.81 to 1.75 mequiv/g. The corresponding water uptakes and dimensional changes were in the ranges of 19–42% and 12–38%, respectively. The tensile strength of an AEM (1.75MQAPES-OH) with an IEC of 1.75 mequiv/g remained 17 MPa even though the water uptake was 42%. The hydroxide conductivity of 1.75MQAPES-OH could reach 51.4 mS/cm at 98%RH and 80 °C. After alkaline stability test for 168 h, the AEMs degraded slightly in terms of their IECs and hydroxide conductivity.

The following sections are included: Introduction XAS for CO2 Reduction Electrochemical CO2 Reduction Photochemical CO2 Reduction Summary and Proposed Research Prospects Acknowledgments ReferencesThe following sections are included: Introduction XAS for CO2 Reduction Electrochemical CO2 Reduction Photochemical CO2 Reduction Summary and Proposed Research Prospects Acknowledgments References

Ascertaining the function of in-plane intrinsic defects and edge atoms is necessary for developing efficient low-dimensional photocatalysts. We report the wireless photocatalytic CO2 reduction to CH4 over reconstructed edge atoms of monolayer 2H-WSe2 artificial leaves. Our first-principles calculations demonstrate that reconstructed and imperfect edge configurations enable CO2 binding to form linear and bent molecules. Experimental results show that the solar-to-fuel quantum efficiency is a reciprocal function of the flake size. It also indicates that the consumed electron rate per edge atom is two orders of magnitude larger than the in-plane intrinsic defects. Further, nanoscale redox mapping at the monolayer WSe2–liquid interface confirms that the edge is the most preferred region for charge transfer. Our results pave the way for designing a new class of monolayer transition metal dichalcogenides with reconstructed edges as a non-precious co-catalyst for wired or wireless hydrogen evolution or CO2 reduction reactions.

Abstract Atomically dispersed iron sites on nitrogen-doped carbon (Fe-NC) are the most active Pt-group-metal-free catalysts for oxygen reduction reaction (ORR). However, due to oxidative corrosion and the Fenton reaction, Fe-NC catalysts are insufficiently active and stable. Herein, w e demonstrated that the axial Cl-modified Fe-NC (Cl-Fe-NC) electrocatalyst is active and stable for the ORR in acidic conditions with high H2O2 tolerance. The Cl-Fe-NC exhibits excellent ORR activity, with a high half-wave potential (E1/2) of 0.82 V versus a reversible hydrogen electrode (RHE), comparable to Pt/C (E1/2 = 0.85 V versus RHE) and better than Fe-NC (E1/2 = 0.79 V versus RHE). X-ray absorption spectroscopy analysis confirms that chlorine is axially integrated into the FeN4. More interestingly, compared to Fe-NC, the Fenton reaction is markedly suppressed in Cl-Fe-NC. In situ electrochemical impedance spectroscopy reveals that Cl-Fe-NC provides efficient electron transfer and faster reaction kinetics than Fe-NC. Density functional theory calculations reveal that incorporating Cl into FeN4 can drive the electron density delocalization of the FeN4 site, leading to a moderate adsorption free energy of OH* (?GOH*), d-band center, and a high onset potential, and promotes the direct four-electron-transfer ORR with weak H2O2 binding ability compared to Cl-free FeN4, indicating superior intrinsic ORR activity.

Abstract Effects of electronic and atomic structures of V-doped 2D layered SnS2 are studied using X-ray spectroscopy for the development of photocatalytic/photovoltaic applications. Extended X-ray absorption fine structure measurements at V K-edge reveal the presence of VO and VS bonds which form the intercalation of tetrahedral OVS sites in the van der Waals (vdW) gap of SnS2 layers. X-ray absorption near-edge structure (XANES) reveals not only valence state of V dopant in SnS2 is ≈4+ but also the charge transfer (CT) from V to ligands, supported by V Lα,β resonant inelastic X-ray scattering. These results suggest V doping produces extra interlayer covalent interactions and additional conducting channels, which increase the electronic conductivity and CT. This gives rapid transport of photo-excited electrons and effective carrier separation in layered SnS2. Additionally, valence-band photoemission spectra and S K-edge XANES indicate that the density of states near/at valence-band maximum is shifted to lower binding energy in V-doped SnS2 compare to pristine SnS2 and exhibits band gap shrinkage. These findings support first-principles density functional theory calculations of the interstitially tetrahedral OVS site intercalated in the vdW gap, highlighting the CT from V to ligands in V-doped SnS2.