Mass Transport Behavior Research Articles

From Catalyst Coated Membranes to Porous Transport Electrode Based Configurations in PEM Water Electrolyzers

So far the superior cell polarization behavior of membrane electrode assemblies (MEAs) using catalyst coated membranes (CCMs) as compared to those using porous transport electrodes (PTEs) was a paradigm in proton exchange membrane water electrolyzers (PEMWEs). However, this paradigm was so far neither systematically investigated nor understood. In this study, we investigate the changes in PEMWE polarization behavior upon gradually changing the MEA from a full CCM toward a full PTE-type configuration. We explain all observed findings based on the idea for a structural model of discontinuous catalyst layers. Our results show, that for current densities above 750 mA cm−2, PTE-based MEAs can result in a better polarization behavior than CCMs. Therefore, the prevailing paradigm was disproved. CCMs showed better kinetics, while PTE-type configurations performed more reproducible than CCMs despite rougher surfaces. Due to the trend of a stabilizing HFR-free cell voltage, an improved mass transport behavior of the PTE-type configurations at high current densities is assumed. Within the error-tolerance, no clear differences between PTE and CCM-based configurations in ohmic resistance could be determined. We conclude that PTE-based configurations for PEMWE, as alternatives to standard CCM-configurations, could be highly important for future manufacturing techniques depending on the application's needs.

Axial mixing and vortex stability to in situ radial injection in Taylor–Couette laminar and turbulent flows

Taylor–Couette flows have been widely studied in part due to the enhanced mixing performance from the variety of hydrodynamic flow states accessible. These process improvements have been demonstrated despite the traditionally limited injection mechanisms from the complexity of the Taylor–Couette geometry. In this study, using a newly designed, modified Taylor–Couette cell, axial mass transport behaviour is experimentally determined over two orders of magnitude of Reynolds number. Four different flow states, including laminar and turbulent Taylor vortex flows and laminar and turbulent wavy vortex flows, were studied. Using flow visualization techniques, the measured dispersion coefficient was found to increase with increasing $Re$, and a single, unified regression is found for all vortices studied. In addition to mass transport, the vortex structures’ stability to radial injection is also quantified. A dimensionless stability criterion, the ratio of injection to diffusion time scales, was found to capture the conditions under which vortex structures are stable to injection. Using the stability criterion, global and transitional stability regions are identified as a function of Reynolds number, $Re$.

Direct Measurement of Mass Transport in Actuation of Conducting Polymers Nanotubes.

Nanostructured Conducting polymer (CP) actuators are promising materials for biomedical applications such as drug release systems. However, understanding the actuation behavior at the nano-scale has not yet been explored. In this work, poly(3,4-ethylenedioxythiophene) (PEDOT) and poly(pyrrole) (PPy) nanotubes doped with a large counter ion (i.e. poly(styrene sodium sulfonate) (PSS)) were fabricated using electrochemical deposition of PEDOT and PPy around poly(L-lactide) (PLLA) nanofiber templates, followed by template removal in chloroform. The actuation and mass transport behavior of PPy and PEDOT nanotubes were investigated and compared. The nanotubes were subjected to a redox process using cyclic voltammetry in 0.1M NaPSS electrolyte solution as the potential swept between -0.8 V and +0.4 V for 20 cycles at 10, 50, 100, and 200 mV/s scan rates. The mass transport behavior of these nanotubes was characterized via electrochemical quartz crystal microbalance (EQCM) technique. The EQCM results showed that PEDOT nanotubes had a higher mass exchange capability than their PPy counterparts, especially at higher scan rates. Also, it was revealed that PPy nanotubes were more sensitive to the scan rate than the PEDOT nanotubes, and the maximum mass exchange capability of the PPy nanotubes was noticeably reduced by increasing the scan rate.

Pore Structure-Dependent Mass Transport in Flow-through Electrodes for Water Remediation.

Hierarchical three-dimensional architectures of granphene-based materials with tailored microstructure and functionality exhibit unique mass transport behaviors and tunable active sites for various applications. The micro- /nanochannels in the porous structure can act as micro- /nano- reactors, which optimize the transport and conversion of contaminants. However, the size-effects of the micro- /nanochannels, which are directly related to its performance in electrochemical processes, have not been explored. Here, using lamellar-structured graphene films as electrodes, we demonstrate that the interlayer spacing (range from ∼84 nm to ∼2.44 μm) between graphene nanosheets governs the mass transport and electron transfer in electrochemical processes; subsequently influence the water decontamination performances. The microchannel (interlayer spacing = ∼2.44 μm) can provide higher active surface areas, but slow reaction kinetics. Densely packed graphene nanosheets (interlayer spacing = ∼280 nm), which possessed better electron conductivity and could provide higher surface-area-to-volume ratio in narrow nanochannels (7.14 μm-1), achieved the highest reaction kinetics. However, the ion-accessible surface area was decreased in highly dense films (interlayer spacing = ∼84 nm) due to serious interlayer stacking of graphene nanosheets, thereby leading poor reaction kinetics. These results demonstrate the size-effect of nanochannels in porous materials and highlight the importance of controlling mass transport and electron transfer for optimal electrochemical performance, enabling a deep understanding of the benefits and utilization of these hierarchical three-dimensional architectures in water purification.

Modeling of coupled thermal-hydraulic-mechanical-chemical processes for predicting the evolution in permeability and reactive transport behavior within single rock fractures

A multi-physics numerical model was developed to predict the fluid flow and mass transport behavior of rock fractures under coupled thermal-hydraulic-mechanical-chemical (THMC) conditions. In particular, the model was employed for the purpose of describing the evolution of permeability and reactive transport behavior within rock fractures by taking into account the geochemical processes of the free-face dissolution and the pressure dissolution. In order to examine the capability of the developed model, the model was applied to replicate the experimental measurements of the evolution in hydraulic aperture, permeability, and element concentrations obtained from two flow-through experiments using single granite and mudstone fractures. The model predictions for the granite experiment were able to follow the actual data for the evolution in hydraulic aperture and effluent element concentrations without adopting any fitting parameters that are often used in other THMC coupled models obtained from literature. Furthermore, the model succeeded in replicating the actual changes in fracture permeability and effluent element concentrations within the mudstone fracture. Although some uncertain mismatches between the experiments and the model predictions, such as changes in the concentrations of several elements (i.e., Na and K concentrations in the granite fracture and Al in the mudstone fracture) were remaining at this stage, the developed model should be valid for evaluating the evolution in the fluid flow and mass transport behavior within rock fractures induced by mineral dissolution under stress- and temperature-controlled conditions.

Characteristics of multiscale mass transport and coordination mechanisms for shale gas

Multiscale mass transport behavior is obvious during shale gas development. Considering multiscale pore structure, multiple gas transport mechanisms and multiple micro effects, a unified mathematical model of shale equivalent permeability was constructed. Then the characteristics of shale permeability during a real production process was analyzed. The main impacts of multiscale mass transport of shale gas was investigated, including gas-solid properties, pore geometry and its connectivity, and temperature and pressure conditions. An evaluation index of multiscale mass transport behavior of shale gas was then put forward, which was the proportion of pores with diameter between 50 and 200 nm. A specific methodology on evaluating multiscale mass transport of shale gas was presented based on mesoscience. Considering the main problems in shale gas development, the coordination mechanisms for multiscale mass transport processes was put forward, which includes controlling water phase trapping damage, enlarging and connecting nanopores in matrix, and accelerating gas desorption-diffusion.

Polydopamine coating on a thin film composite forward osmosis membrane for enhanced mass transport and antifouling performance

We applied a polydopamine (PDA) coating on a thin film composite (TFC) forward osmosis (FO) membrane and investigated the effects of coating on FO mass transport and antifouling behavior. The PDA coating significantly improved membrane surface hydrophilicity as well as reduced membrane surface roughness. Using a short PDA coating duration of 0.5 h, the coated membrane TFC-C0.5 achieved enhanced FO water flux and reduced reverse solute diffusion simultaneously. The reduced reverse solute diffusion can be attributed to the enhanced membrane selectivity: TFC-C0.5 had better rejection and similar water permeability compared to the original TFC membrane. This reduction in reverse solute diffusion further reduced the internal concentration polarization inside the coated membrane, leading to an enhanced FO water flux. Nevertheless, longer PDA coating duration of 1–4 h resulted in reduced FO water flux due to the significantly increased hydraulic resistance of the coated membranes. The PDA coated membrane TFC-C0.5 also presented an improved antifouling performance compared to the control membrane using alginate as a model foulant. Our results reveal the great room for the development of effective coating materials in FO: a well-designed coating with high selectivity and low hydraulic resistance can improve solute rejection, reduce reverse solute diffusion, mitigate internal concentration polarization and enhance FO water flux in addition to control fouling. Such unprecedented opportunities break the traditional trade-off between water flux and antifouling performance when coating pressure driven reverse osmosis membranes.

In situ quantitative single-molecule study of dynamic catalytic processes in nanoconfinement

Understanding the fundamental catalytic principles when the catalytic centre is confined in nanoscale space that is dimensionally comparable to the reactant molecule is crucial for designing high-performance catalysts. Theoretical studies with simplified model systems and ensemble experimental measurements have shown that chemical reactions in nanoconfined environments are largely different from those in bulk solution. Here, we design a well-defined platform with catalytic centres confined in the end of nanopores with controlled lengths to study the in situ dynamic behaviour of catalytic processes under nanoconfinement at the single-molecule and single-particle level. Variable single molecular mass transport behaviour reveals the heterogeneity of the confined environment in the nanopores. With the capability of decoupling mass transport factors from reaction kinetics in the well-defined platform, we quantitatively uncovered a confinement-induced enhancement in the activity of platinum nanoparticles inside the nanopores. The combination of the unique model catalyst and the single-molecule super-localization imaging technique paves the way to understanding nanoconfinement effects in catalysis. Nanoconfinement effects are crucial in any process that involves porous materials. Here, the authors present a nanoporous catalyst platform that enables these effects to be studied in situ at the single-molecule and single-particle level with turnover resolution.

Designed cellulose nanocrystal surface properties for improving barrier properties in polylactide nanocomposites

Nanocomposites are an opportunity to increase the performance of polymer membranes by fine-tuning their morphology. In particular, the understanding of the contribution of the polymer matrix/nanofiller interface to the overall transport properties is key to design membranes with tailored selective and adsorptive properties. In that aim, cellulose nanocrystals (CNC)/polylactide (PLA) nanocomposites were fabricated with chemically designed interfaces, which were ensuring the compatibility between the constituents and impacting the mass transport mechanism. A detailed analysis of the mass transport behaviour of different permeants in CNC/PLA nanocomposites was carried out as a function of their chemical affinity to grafted CNC surfaces. Penetrants (O2 and cyclohexane), which were found to slightly interact with the constituents of the nanocomposites, provided information on the small tortuosity effect of CNC on diffusive mass transport. The mass transport of water (highly interacting with CNC) and anisole (interacting only with designed CNC surfaces) exhibited non-Fickian, Case II behaviour. The water vapour caused significant swelling of the CNC, which created a preferential pathway for mass transport. CNC surface grafting could attenuate this phenomenon and decrease the water transport rate. Anisole, an aromatic organic vapour, became reversibly trapped at the specifically designed CNC/PLA interface, but without any swelling or creation of an accelerated pathway. This caused the decrease of the overall mass transport rate. The latter finding could open a way to the creation of materials with specifically designed barrier properties by designing nanocomposites interfaces with specific interactions towards permeants.

Recent Advances in the Fabrication of Membranes Containing "Ion Pairs" for Nanofiltration Processes.

In the face of serious environmental pollution and water scarcity problems, the membrane separation technique, especially high efficiency, low energy consumption, and environmental friendly nanofiltration, has been quickly developed. Separation membranes with high permeability, good selectivity, and strong antifouling properties are critical for water treatment and green chemical processing. In recent years, researchers have paid more and more attention to the development of high performance nanofiltration membranes containing “ion pairs”. In this review, the effects of “ion pairs” characteristics, such as the super-hydrophilicity, controllable charge character, and antifouling property, on nanofiltration performances are discussed. A systematic survey was carried out on the various approaches and multiple regulation factors in the fabrication of polyelectrolyte complex membranes, zwitterionic membranes, and charged mosaic membranes, respectively. The mass transport behavior and antifouling mechanism of the membranes with “ion pairs” are also discussed. Finally, we present a brief perspective on the future development of advanced nanofiltration membranes with “ion pairs”.

Simulation of Stresses Induced by Heat and Mass Transfer in Drying Process of Clay-like Material

Drying represents one of the oldest unit operations employed in industrial processes. Drying is viewed as a process of simultaneous heat and mass transfer. Porous Clay-like material undergoes stresses due to non-uniform distribution of temperature and moisture induced by heat and mass transfer respectively. The aim of this work is to simulate the stresses induced by heat and mass transfer during drying. A mathematical model to simulate the convective drying of a porous material like clay has been developed. The problem investigated involves highly coupled equations considering heat, mass, and mechanical aspects. The particularity of the model is that it takes into account the strong coupling between mass transport, heat transport and mechanical behavior of the material. The variables of coupling are the solid deformation, moisture content and temperature of porous medium. A numerical solution is sought to foresee the variation of moisture content, temperature, shrinkage, heat transfer induced stresses and mass transfer induced stresses during drying. The solution developed as a model is capable of predicting the quality of the product through a failure criterion. The model is validated through the comparison of simulated and experimental data. Simulation results show that the heat transfer induced stresses are significantly less important in compression with the mass transfer induced stresses and can be neglected in modeling of drying process.

Effect of frictional heating on mixed convection flow of chemically reacting radiative Casson nanofluid over an inclined porous plate

The present study deals with the boundary layer analysis of a 2D magnetohydrodynamic flow of chemically reacting Casson nanofluid flow over a semi-infinite inclined porous plate. The energy and diffusion equation are encompassed with frictional heating, heat generation/absorption, thermo diffusion and thermal radiation effects. For making the analysis more attractive we pondered two distinct type of nanofluids namely, TiO2-water and CuO-water. The transmuted governing PDEs are resolved analytically by employing regular perturbation method. The impact of pertinent flow parameters on momentum, thermal and mass transport behavior including the skin friction factor, thermal and mass transport rate are examined and published with the assistance of graphical and tabular forms. Results describe that thermal radiation and chemical reaction restrictions have a propensity to enhance thermal and mass transport rates, respectively. And also, water based TiO2 nanofluid possess higher velocity compared with water based CuO nanofluids.

Carbon nanotube- and graphene-based advanced membrane materials for desalination

The development of membrane-based desalination and water purification technologies offers new alternatives to meet the global freshwater demand. Rapid advancement in carbon nanotube-based and graphene-based nanomaterials has drawn the attention of scientific investigators on various desalination technologies. These nanomaterials indeed offer advantageous structure, size, shape, porosity and mass transport behavior for membrane separation process. This article reviews theoretical and experimental investigations of carbon nanotube- and graphene-based composite materials for desalination. Special attention is given to the simulation of molecular transport through these materials. Further, recent advances in the application of functionalization of carbon nanotube- and graphene-based materials for salt rejection and hydraulic permeation properties are discussed.

Stochastic Generation of Sintered Titanium Powder-Based Porous Transport Layers in Polymer Electrolyte Membrane Electrolyzers and Investigation of Structural Properties

One of the factors leading to a decrease in the efficiency of polymer electrolyte membrane (PEM) electrolyzers is the blockage of water transport pathways through the porous transport layer (PTL). The oxygen bubbles generated from the electrochemical reaction at the catalyst layer accumulate in the PTL, impeding the transport pathways and reaction sites for the reactant water (1). An improved understanding of oxygen bubble accumulation and water transport behaviour in porous transport layers is essential to reduce mass transport losses in PEM electrolyzers. This study presents a method to stochastically generate a PTL composed of sintered titanium (Ti) powders and investigate the transport properties using pore network modeling. A microscale X-ray computed tomography (µ-CT) was performed for a sintered Ti powder PTL sample to obtain a 2D density map. The density map contains material content information, providing higher intensity at the positions with higher material content. With the density map as an input, a stochastic model of the PTL was generated by placing Ti powder particles at positions decided by the density map and a probability function until the model reached the target volume (2). Two critical parameters are considered in this model: the seeding parameter, α, and a filling radius, β. The seeding parameter controls the number of Ti powder “seeds” that act as nucleation sites. The second parameter, the filling radius, allows the model to mimic the morphology of the sintered regions. The structural properties of the stochastic model are investigated by comparing the pore size distribution, throat size distribution, and the porosity profile to the µ-CT reconstruction. Pore network modeling is an alternative to continuum modeling for simulating transport in porous media. Pore network modeling simplifies the solution of differential equations for mass transport by treating the pore space as a network of pores and narrow throats (3). Using pore network modeling as the analysis tool, the in-plane permeabilities of the µ-CT reconstruction and the stochastic model were compared. The stochastic modeling of PTLs will facilitate the detailed parametric studies of PTL structural property impacts on transport and provide novel insights into mass transport behavior in PEM electrolyzers.References H. Ito, T. Maeda, A. Nakano, Y. Hasegawa, N. Yokoi, C. M. Hwang, M. Ishida, A. Kato, and T. Yoshida, International journal of hydrogen energy 35(18), 9550-9560 (2010). A. Ebrahimi Khabbazi, J. Hinebaugh, A. Bazylak, Science Bulletin, 61(8), 601-611(2016).A. Putz, J. Hinebaugh, M. Aghighi, H. Day, A. Bazylak, and J. T. Gostick, ECS Transactions, 58(1), 79-86 (2013).

Characterizing the Tortuosity of Aligned Pores and Its Effects on Electrode Kinetics in Directionally Freeze-Cast Cathodes

The prevailing electrode fabrication method for lithium-ion battery electrodes includes calendering at high pressures to densify the electrode and promote adhesion to the metal current collector. However, this process also increases the tortuosity of the pore network in the primary transport direction. In practice, to meet operational C-rates desired, and production throughput objectives, the thicknesses of commercial electrodes are restricted to less than ~100 µm, and the areal capacity to less than ~3.5 mAh/cm2.[ 1 ] With the aim of increasing cell energy density and decreasing cost by building thicker electrodes, several strategies to reduce pore tortuosity in the direction normal to the current collector have been proposed.[ 2-4 ] While improvements in the electrode transport and usable area capacity have been demonstrated when the pore tortuosity is reduced, specific correlations to pore tortuosity have been lacking. Here, we use freeze-casting, a shaping technique able to produce low-tortuosity structures by using ice crystals as a pore-forming agent, to fabricate LiNi0.8Co0.15Al0.05O2(NCA) porous cathodes with a wide range of pore topologies. Two complementary approaches were then used to evaluate the tortuosity of these electrodes. In the first approach, the electrodes were scanned using synchrotron X-ray micro-tomography, and a heat transfer simulation based on a voxel algorithm was directly applied to the 2D binarized image sequence. This algorithm mimics mass transport and diffusion behavior by computing and solving Fourier’s law equations directly across the voxel domain of the porous phase. The second approach used direct current (DC) measurements of polarization and depolarization kinetics to determine the lithium ion diffusivity of the electrolyte-infused porous electrodes. Finally, the electrochemical performance of the electrodes were evaluated in half-cells. The results allow comparison across a wide range of microstructures, and highlight the large impact of a relatively small numerical change in tortuosity on electrode kinetics. Under galvanostatic discharge, the lowest-tortuosity microstructures showed a three- to fourfold increase in area-specific capacity (15 mAh/cm2 at C/10 rate and >5 mAh/cm2 at 1C rate) compared to typical Li-ion composite electrodes. Hybrid pulse power characterization (HPPC) demonstrated improved power capability (150 mW/cm2 to 95 mW/cm2), while dynamic stress tests (DST) showed that an area-specific area capacity of 11.5 mAh/cm² could be reached with a lower discharge voltage limit of 2.5V, corresponding to 91% of the NCA theoretical capacity. This work was supported by the Assistant Secretary for Energy Efficiency and Renewable Energy, Office of Vehicle Technologies of the U.S. Department of Energy under Contract No. DE-AC02-05CH11231, Subcontract No. 7056592 under the Advanced Battery Materials Research (ABMR) Program.

Non-Fickian mass transfer in swelling polymeric non-porous membranes

The aim of this contribution is to formulate a model that investigates the probable occurrence of non-Fickian behavior of mass transport in a viscoelastic polymeric non-porous membrane that swells. Using both continuum mechanics and non-equilibrium thermodynamics approaches, we derive a set of coupled time evolution equations that explicitly incorporate the stress-diffusion mutual interaction. In this 3-D macroscopic model, the trace Π (i.e. the polymer elastic osmotic pressure) and traceless [σp] parts of the polymer second order stress tensor σp serve as the structural independent state variables. In the one dimensional setting, scaling analysis leads to the emergence of three relevant groups of physical parameters namely the core and surface diffusion Deborah numbers De and Deb and a diffusion-stress coupling constant E0 whose effects are examined for both sorption and permeation unsteady processes. We have solved numerically the 1-D governing equations expressed in the material coordinates and obtained profiles for the solvent concentration, non-Fickian diffusion mass flux, stress distribution, swelling, mass-uptake and stress-uptake. The model is capable of predicting a wide range of non-Fickian behaviors, including the two-stage and overshoot cases; and the confrontation with experimental data selected from the literature shows a good agreement.

Unravelling the Surface Structure of MgMn2O4 Cathode Materials for Rechargeable Magnesium-Ion Battery

The spinel MgMn2O4, a cathode material with theoretical capacity of 272 mA h g–1, holds promise for future application in high volumetric magnesium-ion batteries. Atomic-resolution imaging of the structure of the spinel and its surface composition would advance our understanding on its electrochemical properties, mass, and charge transport behavior in electrodes. We observe directly, by aberration-corrected scanning transmission electron microscopy (STEM), the atomic structure of cubic spinel MgMn2O4 for the first time. More importantly, we find that a thin stable surface layer of rocksalt MgMnO2 was grown on a bulk cubic spinel phase. The formation of a rocksalt phase was induced by reconstruction of the spinel phase, i.e., the insertion of Mg into the spinel lattice together with Mg/Mn cation exchange and Frenkel-defect-mediated relocation of Mg cations. This new structural analysis provides a critical step toward understanding and tuning the electrochemical performance of spinel oxide in rechargeable M...

Transport and flow characteristics of an oscillating cylindrical fiber for total artificial lung application

Mass transport and fluid dynamics characteristics in the vicinity of an oscillating cylindrical fiber with an imposed pulsatile inflow condition are computationally investigated in the present study. The work is motivated by a recently proposed design modification to the Total Artificial Lung (TAL) device, which is expected to provide better gas exchange. Navier–Stokes computations, coupled with convection–diffusion equation are performed to assess flow dynamics and mass transport behavior around the oscillating fiber. The oscillations and the pulsatile free stream velocity are represented by two sinusoidal functions. The resulting non-dimensional parameters are Keulegan–Carpenter number (KC), Schmidt number (Sc), Reynolds number (Re), pulsatile inflow amplitude (), and amplitude of cylinder oscillation (). Results are computed for , Sc = 1000, Re = 5 and 10, and 0.7 and 0.25 5.25. The pulsatile inflow parameters correspond to the flow velocities found in human pulmonary artery while matching the operating TAL Reynolds number. Mass transport from the surface of the cylinder to the bulk fluid is found to be primarily dependent on the size of surface vortices created by the movement of the cylinder. Time-averaged surface Sherwood number (Sh) is dependent on the amplitude and KC of cylinder oscillation. Compared to the fixed cylinder case, a significant gain up to 380% in Sh is achieved by oscillating the cylinder even at the small displacement amplitude (AD = 0.75D). Moreover, with decrease in KC the oscillating cylinder exhibits a lower drag amplitude compared with the fixed cylinder case. Inflow pulsation amplitude has minor effects on the mass transport characteristics. However, an increase in results in an increase in the amplitude of the periodic drag force on the cylinder. This rise in the drag amplitude is similar to that measured for the fixed cylinder case. Quantifications of shear stress distribution in the bulk fluid suggest that the physiological concerns of platelet activation and injury to red blood cells due to cylinder oscillation are negligible.

Quantitative and mechanistic analysis of impact of novel cassava-assisted improved processing on fluid transport phenomenon in humidity-temperature-stressed bio-derived films

Bio-derived films’ realistic performance integrity is ascertained by their resilience in highly-stressful storage conditions, a function of its ability to respond timely and manages fluid barrier appropriately. Bio-derived films’ moisture and temperature sensitivity often posed mass transport challenges, thus decreasing their lifespan. Quantifying bio-derived film mass transport behaviour has been limited to mass transfer representations, which can be imperfect to understand fully mass transport phenomenon. This study reported quantitative and mechanistic analysis of fluid-phase mass transport phenomenon in Simultaneous Release Recovery Cyanogenesis-produced intact bitter cassava (IBC) bio-derived films under stressful conditions. Films were tested for solvent solubility, swelling ratio, sorption and permeability to water vapour and oxygen at 10–40°C and 10–95% RH. Film’s structural alterations were characterised by their thermal and chemical properties. Modified-BET, Peleg, Oswin models best described sorption data. Temperature-dependence of film water vapour permeability was simulated best by Arrhenius model, while oxygen permeability was influenced highly by crystallinity and RH. Non-organic and organic film-solvent diffusion followed case II and Fickian diffusional patterns respectively. Solvents induced structural changes in IBC films with concentration-dependent diffusion. Cassava bio-derived films’ integrity will depend on the host environment, thus maximum care should be ensured to minimise environment impact during applications. Nonetheless, IBC films hold potential as biomaterials for broad range product use.

Interplay Between Chemical and Optoelectronic Properties of III/V-Water Interfaces from Ab Initio Simulations

Photoelectrochemical cells promise sustainable production of hydrogen fuel from water using sunlight, mimicking natural photosynthetic processes. However, finding light-absorbing semiconductor photoelectrode materials that are suitably efficient and also durable under operation has proven challenging. This is largely because electrode durability and efficiency are extremely sensitive to the chemistry at the interface between liquid water and the semiconductor, which is often extraordinarily difficult to probe under operating conditions. In this talk, I will illustrate how ab initio methods have been applied to understand the complex chemistry active at the interface of water with III-V semiconductor photocathodes (GaP, InP, and GaInP2), which offer among the highest solar-to-hydrogen conversion efficiencies but suffer from durability shortcomings. I will show how large-scale ab initio molecular dynamics simulations have assisted in determining the dependence of the available chemical pathways on the surface structure and composition of these materials. I will also show how dynamics simulations can be coupled to many-body perturbation theory to directly probe the link between macroscopic optoelectronic properties and local interfacial chemistry, which is necessary for devising meaningful interface optimization strategies. Finally, I will discuss how combining X-ray photoelectron spectroscopy (XPS) simulations with near-ambient-pressure XPS experiments can identify interfacial chemical speciation under operating conditions. Key differences between InP and GaP will be highlighted, including how different chemistry and mass transport behavior at the interface with water impact relative stability and efficiency. Specific implications for understanding the performance and durability of III-V photocathodes will be discussed, along with some general insights for engineering photoelectrochemical interfaces. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.