Compressed composite carbon felt as a negative electrode for a zinc-iron flow battery.

Flow batteries possess several attractive features including long cycle life, flexible design, ease of scaling up, and high safety. They are considered an excellent choice for large-scale energy storage. Carbon felt (CF) electrodes are commonly used as porous electrodes in flow batteries. In vanadium flow batteries, both active materials and discharge products are in a liquid phase, thus leaving no trace on the electrode surface. However, zinc-based flow batteries involve zinc deposition/dissolution, structure and configuration of the electrode significantly determine stability and performance of the battery. Herein, fabrication of a compressed composite using CF with polyvinylidene fluoride (PVDF) is investigated in a Zn-Fe flow battery (ZFB). Graphene (G) is successfully introduced in order to improve its electrochemical activity towards zinc reactions on the negative side of the ZFB. A compressed composite CF electrode offers more uniform electric field and lower nucleation overpotential (NOP) of zinc than a pristine CF, resulting in higher zinc plating/stripping efficiency. Batteries with modified electrodes are seen to provide lower overpotential. Particularly, the G-PVDF-CF electrode demonstrates maximum discharge capacity of 39.6 mAh cm-2 with coulombic efficiency and energy efficiency over 96% and 61%, respectively. Finally, results lead to increased efficiency and cycling stability for flow batteries.

Beyond the Phase Segregation: Probing the Irreversible Phase Reconstruction of Mixed-Halide Perovskites.

Mixed-halide perovskites can undergo a photoinduced phase segregation. Even though many reports have claimed that such a phase segregation process is reversible, what happens after phase segregation and its impact on the performance of perovskite-based devices are still open questions. Here, the phase transformation of MAPb(I1- x Brx )3 after phase segregation and probe an irreversible phase reconstruction of MAPbBr3 is investigated. The photoluminescence imaging microscopy technique is introduced to in situ record the whole process. It is proposed that the type-I band alignment of segregated I-rich and Br-rich domains can enhance the emission of the I-rich domains by suppressing the nonradiative recombination channels. At the same time, the charge injection from Br-rich to I-rich domains drives the expulsion of iodide from the lattice, and thus triggers the reconstruction of MAPbBr3 . The work highlights the significance of ion movements in mixed-halide perovskites and provides new perspectives to understand the property evolution.

A Ladder-like Dopant-free Hole-Transporting Polymer for Hysteresis-less High-Efficiency Perovskite Solar Cells with High Ambient Stability.

Perovskite solar cells (PSCs) have received high attention in the past few years due to their terrific photovoltaic performance and potentially low production cost. However, the use of hole transport materials (HTMs) with hygroscopic dopants, which cause the inevitable instability of device performance, has hampered commercialization. Herein, a dopant-free polymeric HTM with functional aromatic rings was used to optimize the HTM/perovskite interface and employed in a planar n-i-p configuration. Poly(1,4-(2,5-bis((2-butyloctyloxy)phenylene)-2,7-(5,5,10,10-tetrakis(4-hexylphenyl)-5,10-dihydro-s-indaceno[2,1-b:6,5-b']dithiophene)) (IDTB) co-polymer constructed with indaceno[1,2-b:5,6-b']dithiophene and bis(alkyloxy)benzene units adopts an S⋅⋅⋅O intramolecular bond linked ladder-like planar conjugated polymer backbone. Without any dopant, the hole mobility of IDTB is in the same order of magnitude as a doped 2,2',7,7'-tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (spiro-OMeTAD). Also, the hydrophobic nature of IDTB facilitated the long-term stability of the perovskite underneath. The unencapsulated PSC devices made of IDTB-based HTM achieved a power conversion efficiency of 19.38 % with a high moisture stability, retaining above 80 % of initial power conversion efficiency at 65 % relative humidity for more than 10 days. The superior passivation effect to perovskite surface made a hysteresis of 0.44 % was almost the least reported for regular planar undoped polymer HTM PSCs.

Discharge profile of a zinc-air flow battery at various electrolyte flow rates and discharge currents.

Nowadays, due to global warming stemming from excessive use of fossil fuel, there is considerable interest in promoting renewable energy sources. However, because of the intermittent nature of these energy sources, efficient energy storage systems are needed. In this regard, zinc-air flow batteries (ZAFBs) are seen as having the capability to fulfill this function. In flow batteries, the electrolyte is stored in external tanks and circulated through the cell. This study provides the requisite experimental data for parameter estimation as well as model validation of ZAFBs. Each data set includes: current (mA), voltage (V), capacity (mAh), specific capacity (mAh/g), energy (Wh), specific energy (mWh/g) and discharge time (h:min:s.ms). Discharge data involved forty experiments with discharge current in the range of 100-200 mA, and electrolyte flow rates in the range of 0-140 ml/min. Such data are crucial for the modelling and theoretical/experimental analysis of ZAFBs.

Linear parameter-varying model for a refuellable zinc-air battery.

Due to the increasing trend of using renewable energy, the development of an energy storage system (ESS) attracts great research interest. A zinc-air battery (ZAB) is a promising ESS due to its high capacity, low cost and high potential to support circular economy principles. However, despite ZABs' technological advancements, a generic dynamic model for a ZAB, which is a key component for effective battery management and monitoring, is still lacking. ZABs show nonlinear behaviour where the steady-state gain is strongly dependent on operating conditions. The present study aims to develop a dynamic model, being capable of predicting the nonlinear dynamic behaviour of a refuellable ZAB, using a linear parameter-varying (LPV) technique. The LPV model is constructed from a family of linear time-invariant models, where the discharge current level is used as a scheduling parameter. The developed LPV model is benchmarked against linear and nonlinear model counterparts. Herein, the LPV model performs remarkably well in capturing the nonlinear behaviour of a ZAB. It significantly outperforms the linear model. Overall, the LPV approach provides a systematic way to construct a robust dynamic model which well represents the nonlinear behaviour of a ZAB.

Understanding Degradation Mechanisms and Improving Stability of Perovskite Photovoltaics.

This review article examines the current state of understanding in how metal halide perovskite solar cells can degrade when exposed to moisture, oxygen, heat, light, mechanical stress, and reverse bias. It also highlights strategies for improving stability, such as tuning the composition of the perovskite, introducing hydrophobic coatings, replacing metal electrodes with carbon or transparent conducting oxides, and packaging. The article concludes with recommendations on how accelerated testing should be performed to rapidly develop solar cells that are both extraordinarily efficient and stable.

In Situ Measurement of Electric-Field Screening in Hysteresis-Free PTAA/FA0.83Cs0.17Pb(I0.83Br0.17)3/C60 Perovskite Solar Cells Gives an Ion Mobility of ∼3 × 10-7 cm2/(V s), 2 Orders of Magnitude Faster than Reported for Metal-Oxide-Contacted Perovskite Cells with Hysteresis.

We apply a series of transient measurements to operational perovskite solar cells of the architecture ITO/PTAA/FA0.83Cs0.17Pb(I0.83Br0.17)3/C60/BCP/Ag, and similar cells with FA0.83MA0.17. The cells show no detectable JV hysteresis. Using photocurrent transients at applied bias we find a ∼1 ms time scale for the electric field screening by mobile ions in these cells. We confirm our interpretation of the transient measurements using a drift-diffusion model. Using Coulometry during field screening relaxation at short circuit, we determine the mobile ion concentration to be ∼1 × 1018/cm3. Using a model with one mobile ion species, the concentration and the screening time require an ion mobility of ∼3 × 10-7 cm2/(V s). As far as we know, this article gives the first direct measurement of the ion mobility and concentration in a fully functional perovskite solar cell. The measured ion mobility is 2 orders of magnitude higher than the highest estimates previously determined using perovskite solar cells and perovskite thin films, and 3 orders of magnitude higher than is frequently used in modeling hysteresis effects. We provide evidence that the fast field screening is due to mobile ions, as opposed to dark injection and trapping of electronic carriers.