Mass Transfer Limitations Research Articles

Supercritical Fluids for Enhanced Chemical Transformation of Postconsumer Plastics: A Review

Various chemical transformation approaches are being actively developed to address the environmental accumulation of plastic waste. However, most postconsumer plastics are heterogeneous, exhibit high melt viscosity, and are insoluble in most conventional solvents. Such properties result in transport‐limiting chemical transformations, resulting in low conversion rates, and low product selectivity. Although supercritical fluids (SCFs) have been a matter of continuing scientific interest in several mass‐transfer processes, the use of SCFs as tunable media for the chemical transformation of postconsumer plastics is still in its early stages, but has rapidly advancing in recent years. Therefore, this review reports on the current state‐of‐art of chemical transformation of plastics using SCFs. It addresses the effects of sub‐and supercritical CO2 (scCO2) on solvolysis‐based technologies. Also, it reviews recent advances on the use of supercritical organic solvents (e.g., ethanol, methanol) and supercritical water (SCW) as reaction media for the solvolysis and liquefaction of plastics, respectively, and the latest developments in the simultaneous conversion of CO2 and waste plastics. Overall, developing technologies that minimize mass transfer limitations during chemical transformation of plastics is critical to overcome some of the major bottlenecks hampering product yield and selectively, and ultimately the economic viability of plastics recycling and upcycling.

Efficient synthesis of nanosized zeolite Y utilizing gradual heating: post-synthesis modification and their catalytic performance in propylene oligomerization

Abstract Producing nanosized zeolites Y has been restricted to a Si/Al ratio lower than 2.0, requiring prolonged crystallization periods. This study employed temperature ramps during nucleation and crystallization to synthesize nanosized zeolites Y with a Si/Al ratio of 2.4, ranging from 47 to 100 nm, in just one day. Sequential post-synthesis desilication and dealumination treatments were used to modify the pore structure and acidity of the zeolites, leading to hierarchical zeolite formation. These modifications enhanced the structural stability and porosity of the zeolites while preserving their high crystallinity. Desilicated zeolites, unlike dealuminated ones, possessed straighter and more uniform mesoporous within their crystals, with diameters smaller than 5 nm. Additionally, successive desilication produced a greater number of intracrystalline mesoporous. The solids obtained from both processes exhibited porosity within the zeolite structure connected to the external surface, potentially improving the mass transfer limitations of the original zeolite due to the lack of mesoporous. Catalysts were prepared using modified nanozeolites for evaluation in the propylene oligomerization reaction. Catalysts based on dealuminated and desilicated nanosized zeolite Y showed high conversions above 20%, especially for dealuminated zeolites with conversions of 50%. Additionally, the catalysts demonstrated selectivity towards hydrocarbons in the C5-C7 range, suggesting better diffusion and access of propylene molecules to the active sites, favoring the formation of medium-sized hydrocarbon fractions. Conversely, the formation of longer hydrocarbon chains (C12+) was not favored, possibly due to insufficient mesoporous for larger molecule diffusion and a distribution of acid sites that encourages the union of longer hydrocarbon chains.

Metabolic Versatility of acetogens in syngas Fermentation: Responding to varying CO availability.

Syngas fermentation using acetogenic bacteria offers a promising route for sustainable chemical production. However, gas-liquid mass transfer limitations and efficient co-utilization of CO and H2 pose significant challenges. This study investigated the kinetics of syngas conversion to acetate by Acetobacterium wieringae and Clostridium species in batch conditions under varying initial CO partial pressures (19 - 110kPa). A. wieringae strains, exhibited superior growth in all gas compositions, with a maximum growth rate of 0.104h-1. The distinct CO, H2, and CO2 consumption patterns revealed metabolic flexibility and adaptation to varying syngas compositions. Notably, A. wieringae strains and C. autoethanogenum achieved complete CO and H2 conversion, with C. autoethanogenum also exhibiting net CO2 uptake. These findings provide valuable insights into the distinct metabolic capabilities of these acetogens and contribute to the development of efficient and sustainable syngas fermentation processes.

Lipase-catalyzed esterification for efficient acylglycerols synthesis in a solvent-free system: Process optimization, mass transfer insights and kinetic modeling.

Acylglycerols are widely used in the food industry due to their antimicrobial, emulsifying and nutritional properties. This study investigated the key reaction parameters, mass transfer mechanisms, and kinetic features of lipase-catalyzed esterification in a solvent-free system. Taguchi method was further employed to explore the relationship between "reaction parameter - yield composition". The results revealed that the maximum selectivity were achieved fror MAG (57.72%), DAG (82.67%) and TAG (79.29%) under different enzymatic conditions. Fatty acid-to-glycerol molar ratio had the greatest impact on DAG selectivity, contributing 38.08% of total impact level. Mass transfer analysis showed that external mass transfer limitation could be effectively overcome at stirring speeds above 600rpm. Kinetic analysis confirmed that the reaction followed the Ping-Pong BiBi mechanism with alcohol and acid inhibition (SSE=0.000643). This work provided a theoretical basis for developing more efficient and selective catalytic processes, aiding in quality control, reactor design, and industrial scale-up.

Highly Permselective Contorted Polyamide Desalination Membranes with Enhanced Free Volume Fabricated by mLbL Assembly.

The permeability-selectivity trade-off in polymeric desalination membranes limits the efficiency and increases the costs of reverse osmosis and nanofiltration systems. Ultrathin contorted polyamide films with enhanced free volume demonstrate an impressive 8-fold increase in water permeance while maintaining equivalent salt rejection compared to conventional polyamide membranes made with m-phenylenediamine and trimesoyl chloride monomers. The solution-based molecular layer-by-layer (mLbL) deposition technique employed for membrane fabrication sequentially reacts a shape-persistent contorted diamine monomer with a trimesoyl chloride monomer, forming highly cross-linked, dense polyamide networks while avoiding the kinetic and mass transfer limitations of traditional interfacial polymerization. The mLbL process allows precise nanoscale control over polyamide selective layer thickness, network structure, and surface roughness. The resulting controlled film thicknesses enable direct measurements of water and NaCl permeabilities. The permselectivities of contorted polyamide membranes surpass those of commercial desalination membranes and approach the reported polyamide upper bound. Solution-diffusion transport modeling indicates that this high permselectivity may be attributed to enhanced water transport pathways in the contorted polyamides that increase water diffusivity-permeability while maintaining high solute rejection through solubility-selectivity.

Oxidative degradation of lignin by biomass-mediated hierarchical ZSM-5 zeolites: Cβ-O bond breaking and mechanistic analysis.

The catalytic depolymerization of lignin has long been challenged by the limited catalytic mass transfer and the complexity of its polymer structure. In this work, a series of hierarchical MFI nanosheet catalysts (named AL-MFI, M-BKC-MFI, M(metal)-AL-MFI and M(metal)-BKC-MFI, respectively) using biomass (lignin and lignin biochar) as a template were designed to realize the oxidative depolymerization of lignin and its derivatives efficiently and stably. The Zn element in the M-AL-MFI and M-BKC-MFI compensated for the acidity, while Ce could stimulate the production of O2- through redox and trigger a free radical pyrolysis reaction. The conversion rate of lignin was as high as 80.7% and 82.5%, respectively, with acetophenone as the main product in yields as high as 42.82% and 47.13%, respectively. DFT calculations revealed that the bulk sizes of alkali lignin and its derivatives (≤6.112nm) were smaller than the average pore size of the catalysts (≥7.27nm). And this finding provided direct evidence for the critical role of the mesoporous structure of the catalysts in lignin depolymerization. Specifically, the mesoporous structure at suitable acidity contributes to the mass transfer of lignin to the active sites of the catalyst, resulting in an efficient depolymerization process. What's more, the degradation pathways and mechanisms of lignin were analyzed with the help of DFT and GC-MS using 2-phenylethyl phenyl ether (PPE) and 2'-Phenoxyacetophenone (PTE) as model compounds. β-O-4 bonds were broken at a rate of more than 80%, which is the primary mechanism of lignin cleavage. And the order of bond breaking was Cβ-O bond (253J/mol)>Cα-Cβ bond (285.1J/mol)>Caromatic-O bond (407.9 J/mol). M-MFIs promoted the cleavage of Cα-Cβ and Cα-O to a certain extent, which indicated that MFI nanosheets contributed to the cleavage of bonds with higher dissociation energies. This work not only helps to reveal the detailed process of lignin depolymerization, but also provides valuable theoretical guidance for further optimizing the catalyst design and improving the depolymerization efficiency.

The Development of a Novel Aluminosilicate Catalyst Fabricated via a 3D Printing Mold for Biodiesel Production at Room Temperature

Biodiesel production has gained attention as a sustainable alternative to fossil fuels, but challenges related to catalyst recovery and energy consumption remain. In this study, a novel lithium-impregnated aluminosilicate catalyst (LiSA) was developed using a 3D-printed mold, providing precise control over its structure to optimize performance. The structured catalyst featured a cylindrical shape with multiple circular channels, enhancing fluid dynamics and reactant interaction in a fixed-bed reactor. Catalyst characterization by SEM, TGA, XRD, and ICP-MS confirmed high thermal stability and uniform pore distribution. Jatropha curcas oil was used as feedstock, with diethyl ether (DEE) acting as a cosolvent to improve methanol solubility and enable transesterification at room temperature. The process achieved a high fatty acid methyl ester (FAME) yield, averaging 97.1% over 508 min of continuous operation, demonstrating the catalyst’s stability and sustained activity. By reducing mass transfer limitations and energy demands, this approach highlights the potential of 3D-printed catalysts to advance sustainable biodiesel production, offering a scalable and efficient pathway for green energy technologies.

Improving CO2 Capture Efficiency with High-Capacity Solvents: Addressing Temperature-Induced Mass Transfer Limitations

Improving CO₂ Capture Efficiency with High-Capacity Solvents: Addressing Temperature-Induced Mass Transfer Limitations

“Catch-and-feed”: Janus catalytic flow-through membrane enables highly efficient removal of micropollutants in water

Micropollutants, due to their low concentrations, exceptional chemical stability, and profound toxicity, present a significant challenge in water treatment. While electrocatalysis and photocatalysis have shown promise as potential water purification techniques, their inherent limitations in mass transfer often result in elevated energy requirements and suboptimal efficiency. In this study, a Janus catalytic flow-through membrane (JCFM) was utilized to successfully remove two notorious micropollutants dichlorvos (DDVP) and azoxystrobin (AZX) from water based on the "catch-and-feed" strategy. This membrane adopts a "sandwich" configuration, comprising platinum-modified reduced titanium (Pt@rTO) as the electrocatalytic layer, porous titanium (Ti) as the current collector, and rTO as the photocatalytic layer. The JCFM exhibited remarkable performance, maintaining an •OH energy conversion efficiency of up to 20.12 nM and displaying catalytic activity (kJCFM=6.97 × 10–4 s–1) in degrading AZX far superior to that of photocatalysis (kPC=9.51 × 10–5 s–1) or electrocatalysis (kEC=9.89 × 10–5 s–1) alone. It is evidenced that the Pt@rTO layer efficiently generates reactive oxygen species (ROS), which, along with the micropollutants, flow through the JCFM (“feed”), which strengthens mass transfer and facilitates efficient reactions within the confined space (“catch”). The ROSs then seep through the rTO layer, where they are reactivated by UV light radiation. The mechanism and the alternative reaction pathway of DDVP and AZX has also been proposed. In sequential testing, the JCFM achieved continuous and energy-efficient removal of micropollutants, exceeding 97.5% over 200 h. The scale-up application of this technology has proven effective in the treatment of secondary biochemical effluent from municipal sewage, coking wastewater, and landfill leachate, achieving the concurrent degradation of various micropollutants.

Copper catalyzed selective methane oxidation to acetic acid using O2.

The direct transformation of methane into C2 oxygenates such as acetic acid selectively using molecular oxygen (O2) is a significant challenge due to the chemical inertness of methane, the difficulty of methane C-H bond activation/C-C bond coupling and the thermodynamically favored over-oxidation. In this study, we have successfully developed a porous aluminium metal-organic framework (MOF)-supported single-site mono-copper(ii) hydroxyl catalyst [MIL-53(Al)-Cu(OH)], which is efficient in directly oxidizing methane to acetic acid in water at 175 °C with a remarkable selectivity using only O2. This heterogeneous catalyst achieved an exceptional acetic acid productivity of 11 796 mmolCH3CO2H molCu -1 h-1 in 9.3% methane conversion with 95% selectivity in the liquid phase and can be reused at least 6 times. Our experiments, along with computational studies and spectroscopic analyses, suggest a catalytic cycle involving the formation of a methyl radical (˙CH3). The confinement of Cu-active sites within the porous MIL-53(Al) MOF facilitates C-C bond coupling, resulting in the efficient formation of acetic acid with excellent selectivity due to the internal mass transfer limitations. This work advances the development of efficient and chemoselective earth-abundant metal catalysts using MOFs for the direct transformation of methane into value-added products under mild and eco-friendly conditions.

Full recovery of brines at normal temperature with process-heat-supplied coupled air-carried evaporating separation (ACES) cycle

Conventional air-carried evaporating separation (ACES) technology, to achieve complete separation and recovery of water and salt in brine, tends to necessitate heating air above a critical temperature (typically>90 °C). In this paper, a novel concept of process-heat-supplied and an ACES cycle with this technique is proposed. A comprehensive thermodynamic analytical investigation is conducted. The results indicate that at heat source supply temperature Tsupply of only 45.17 °C, this novel unit is capable of achieving complete separation of water and salt from 5 wt% concentration brine. Meanwhile, thermodynamic mechanism analysis reveals that sufficient process-heat-supplied affords the fluid self-adaptive regulation on the driving potential of heat and mass transfer, thus circumventing traditional heat and mass transfer limitation. Additionally, a solar ACES system with process-heat-supplied incorporating heat pump is further proposed. For this system, theoretical evaporation rate for unit area of solar irradiation me-solar = 2.23 kg/(m2·h), integrated solar utilization efficiency ηi = 188%; while considering overall losses me-solar = 1.41 kg/(m2·h), ηi = 95.2%.

Overcoming Gas Mass Transfer Limitations Using Gas-Conducting Electrodes for Efficient Nitrogen Reduction.

Electrocatalytic nitrogen reduction reaction (NRR) is a very attractive strategy for ammonia synthesis due to its energy savings and sustainability. However, the ammonia yield and Faraday efficiency of electrocatalytic nitrogen reduction have been challenges due to low nitrogen solubility and competitive hydrogen evolution reaction (HER) in electrolyte solution. Herein, inspired by the asymmetric wetting behavior, i.e., superhydrophobicity/hydrophilicity, of floating lotus leaves, we demonstrated a gas-conduction electrode with asymmetric gas wetting behavior on the opposite surface, i.e., Janus-Ni/MoO2@NF, for efficient nitrogen reduction. It can provide an abundant three-phase interface (TPI) at interfaces of Janus-Ni/MoO2@NF in electrolyte solution to enhance the contact among N2, electrolyte, and electrode. Ascribed to this advantage, the hydrophobic side of the Janus electrode not only can repel water molecules to suppress the HER process but also can increase the concentration of N2 on the interface microenvironment. Consequently, the well-designed gas-conducting electrode breaks gas mass transfer limitation. Furthermore, Janus-Ni/MoO2@NF delivers a record-high NH3 yield rate of 5.865 μg·h-1·cm-2 and a Faradaic efficiency of 36.14% at an extremely low potential of 0 V vs RHE in 0.1 M Na2SO4 under ambient conditions, which are 22 and 18 times higher than those of the conventional electrode, respectively. Therefore, the gas-conducting electrodes can dramatically improve the activity and selectivity in electrocatalytic NRR. Additionally, the unique interface design provides inspiration for other sustainable electrochemical reactions involving gas electrocatalytic correlation.

The critical role of flocs in nitrification in full-scale aerobic granular sludge-based WWTP.

Aerobic granular sludge (AGS) is usually considered to be a biofilm system consisting of granules only, although practical experience suggests that flocs and granules of various sizes co-exist. This study thus focused on understanding the contribution of flocs and granules of various sizes to nitrification in a full-scale AGS-based wastewater treatment plant (WWTP) operated as a sequencing batch reactor (SBR). The size distribution in terms of total suspended solids (TSS) and the distribution of the nitrifying communities and activities were monitored over 14 months. Our results indicate that AGS is a hybrid system in which flocs (<0.25 mm) play a critical role in nitrification. AGS consisted of 36 % flocs and 50 % large granules (>2 mm) at a TSS concentration of 4.7 ± 0.7 gTSS L-1. The growth of ammonia oxidizing bacteria (AOB) and nitrite oxidizing bacteria (NOB) in large granules was limited due to the high mass transfer limitation in biofilm and the high solids retention time (SRT) of flocs, where favorable conditions for the growth of nitrifiers were maintained during the warm season. The specific activities of the small aggregates (<1 mm) were 5 to 15 times higher than those of large granules. As a result, flocs contributed >50 % to nitrification during the warm season, whereas granules >1 mm contributed <20 %. Such predominance of flocs in nitrification became problematic in the cold season when the minimum SRT of NOB increased to values similar to the floc SRT, resulting in 79 % loss of the NOB. Consequently, NOB activities dropped, and elevated effluent nitrite concentrations of several mgN L-1 were monitored. We suggest operating AGS systems similarly to hybrid systems in order to promote the enrichment of NOB in the granules by controlling the floc SRT at low values smaller than the minimum SRT of NOB throughout the year.

An approach to select between the plausible kinetic models of a heterogeneous catalytic process using intraparticle diffusion with external mass transfer resistance

The reaction rate is sometimes thoroughly described by several kinetic models simultaneously. In this case, the discrimination of the particular model may be challenging. Herein, we demonstrate that a change in the rate-limiting step of a reaction mechanism may result in a significant deviation of the effectiveness factor even if the kinetic rate equations provide nearly identical reaction rates. On this basis, the comparison of the experimental effectiveness factor and the effectiveness factor calculated theoretically using the corresponding rate equations may shed light on the true reaction mechanism. Since many industrial processes operate under internal and external mass transfer limitations, the effectiveness factor is obtained by accounting for pore diffusion resistance and diffusion resistance at the outer surface of a catalyst particle. Verification of the obtained formalism is performed using the kinetic constants for the commercially available process of the methanol dehydration to dimethyl ether over γ-alumina catalyst.

Trichloroethylene detoxification in low-permeability soil via electrokinetic-enhanced bioremediation technology: Long-term feasibility and spatial-temporal patterns

In situ remediation of low-permeability soils contaminated with trichloroethylene (TCE) is challenging due to limited mass transfer and low bioavailability in clay soils. The electrokinetic-enhanced bioremediation (EK-BIO) system offers a promising solution by combining electrokinetics with bioremediation to address these challenges. While previous studies have demonstrated microbial succession and TCE removal, the long-term performance of dechlorination and interactions between electrode reactions and anaerobic dechlorination remain unclear. This study constructed five one-dimensional columns, each operated for a different period (28, 42, 56, 84 and 138 days) to explore spatial and temporal dechlorination patterns. Continuous TCE degradation was achieved, with 46.52 % of TCE recovery. Prolonged electrokinetic operation accelerated the first-step dehalogenation (TCE to DCE). Although Dehalococcoides was widespread at 138 days (2.30–5.74 %), oxygen exposure led to irreversible damage, necessitating secondary inoculation. The presence of aerobic bacteria (Comamonas and Pseudomonas) suggested the formation of aerobic detoxification pathways in electrode chambers. Gene expression analysis (tceA, vcrA and Dhc16S) further confirmed the loss of 2nd and 3rd step dehalogenation (DCE to ethene) over time. These findings demonstrate that secondary inoculation and alternative aerobic pathways can sustain long-term biodegradation in the EK-BIO system. This study highlights the potential of the EK-BIO system for effective remediation of TCE-contaminated low-permeability soils, supporting its field application.

Effect of Reaction Conditions on Nitrogen Conversion During Char-O2/NO Combustion

ABSTRACT Nitrogen conversion during char-O2 combustion with a high initial-NO concentration (char-O2/NO combustion) is an important issue for low-NOx technologies and oxy-fuel combustion technologies, such as air/fuel-staged and flue gas recycling combustion. This study employed both experimental and numerical methods to investigate the mechanisms of N conversion and formation during char-O2/NO combustion. In the numerical model, the mass and heat transfer processes are governed by unsteady convection-diffusion partial differential equations. The numerical results agree well with the experimental findings, assuming NO is the sole primary N-containing product. Based on the numerical results, the effects of reaction conditions on N conversion were decoupled. As the O2/fuel stoichiometric ratio increases, the char-N release rate substantially rises, and the shrinkage of pore surface area becomes significant, leading to poorer NO reduction performance. With an increase in initial-NO concentration, the apparent conversion of char-N to NO decreases, while the NO reduction efficiency remains almost unchanged. Due to the lower temperature sensitivity of mass transfer limitations in the char-NO reaction compared to the char-O2 reaction, NO reduction performance is enhanced at higher reaction temperatures.

Enhancing carbon enrichment by metal-organic cage to improve the electrocatalytic carbon dioxide reduction performance of silver-based catalyst.

Electrochemical reduction of carbon dioxide (CO2) into value-added chemicals provide an alternative technology for achieving carbon neutrality. Limited mass transfer of CO2 in aqueous electrolyte and unsatisfied catalytic activity are the major determinants that inhibit the CO2 conversion at industrial current density level. Herein, an electroreduction-generated metallic Ag atomic clusters supported on metal organic cage (Ag AC/MOC) electrocatalyst is reported to improve the enrichment of inorganic carbon species over catalytic sites for efficient CO2 electroreduction. In-situ infrared spectroscopy and density functional theory studies reveal that the Ag AC/MOC induces the CO2-concentrating in the metal organic cage via a spontaneous ionization of the accumulated CO2, which dramatically enhances the coverage of inorganic carbon species for accelerated kinetic of CO2 conversion. The highly dispersed Ag atomic clusters further reduce the activation energy of CO2 and promote the protonation of CO2 to form carboxyl species, enabling high selectivity toward CO. Hence, the Ag AC/MOC achieves a high CO faradaic efficiency of 97.0%, while the highest CO partial current reaches 231.6mAcm-2, which is significantly higher than that of metallic Ag electrocatalyst. This work demonstrates a deep insight into high-performance electrocatalyst design in view of CO2 transfer and catalytic activity.

A novel flow channel inspired by classical mathematical function: Enhancing output performance and low-grade heat recovery efficiency of thermal regeneration ammonia-based flow battery

Thermal Regeneration Ammonia-based Flow Battery (TRAFB) faces significant challenges in enhancing its output performance and low-grade waste heat recovery efficiency due to limitations in mass transfer and an incomplete understanding of the mass transfer mechanism. To address these issues, this study innovatively introduces a novel sinusoidal wave flow channel (SWFC), which is inspired by the classic mathematical function. The impact of the SWFC on TRAFB performance is thoroughly discussed and compared in detail with the conventional straight flow channel (SFC). Most importantly, this work unveils for the first time the distribution mechanism of the three mass transfer modes in TRAFB, which are convection, diffusion, and electrophoretic mass transfer. The main findings reveal that the mass transfer performance of TRAFB is primarily governed by convection and diffusion, with electrophoretic mass transfer playing a minimal role, and there is a threshold of current density beyond which the dominant mass transfer mechanism transitions from convection to diffusion. The unique design of the SWFC, which induces the Venturi effect, significantly enhances the overall mass transfer performance of the TRAFB due to the distinct local acceleration, achieving a remarkable enhancement in flux of up to 118.48 times. By optimizing the amplitude and period, the battery's output performance can be further enhanced, with the maximum peak power achieved by the SWFC with an amplitude of 0.8 mm and a period of 0.5π, which is 95.63 % over the SFC. Notably, the SWFC also excels in improving the thermoelectric conversion efficiency, particularly at high current densities, achieving an enhancement of up to 9.81 times.

Numerical simulation and experimental study on electrochemical recovery of copper using cylindrical and conical flow reactors

This study investigates the electrochemical recovery of copper from wastewater using cylindrical and conical flow reactors. Electrochemical approaches offer advantages such as environmental compatibility, operational versatility, and energy efficiency for heavy metal remediation. However, effective recovery from dilute effluents remains challenging due to mass transfer limitations. In this work, numerical simulations were conducted to analyze the flow field and current distribution in the reactors, with a focus on the copper reduction process. Experimental results were compared with transient simulations to assess the influence of geometry and operating parameters on the performance of the reactors. The study identified that conical reactors, particularly those with a narrowing electrode gap, enhanced mass transfer rates, leading to improved copper removal efficiency. Key findings include the relationship between electrolyte flow rates, Coulombic efficiency, and copper recovery efficiency. This work contributes to the investigation of electrochemical processes for sustainable heavy metal remediation.

The first implementation of repetitive translucent photocatalyst structures to enhance the energy efficiency of photoelectrochemical applications

Improving the energy efficiency of photoelectrochemical cells (PECs) yields an important tool to address the current carbon circularization problems. However, the efficiency of these cells was held back due to mass, electron, and photon transfer limitations. In this work, the use of translucent repetitive thin catalyst structures within the same light path was introduced in PEC cells, allowing to absorb more irradiated light due to an increased total catalyst loading, while still benefiting from the good transfer phenomena of thin catalyst films. The results unequivocally showed that thinner catalyst layers in a repetitive structure could produce more than seven times the amount of photocurrent than a single thick catalyst layer while utilising less catalyst material. This work proved that not only the nature of the photocatalyst but also the use of repetitive thin translucent structures should be considered when designing a photoelectrochemical reactor to maximise energy efficiency.