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Encapsulation of electrocatalysts and photocatalysts with semipermeable nanoscopic oxide overlayers that exhibit selective transport properties is an attractive approach to achieve high redox selectivity. However, defects within the overlayers─such as pinholes, cracks, or particle inclusions─may facilitate local high rates of parasitic reactions by creating pathways for facile transport of undesired reactants to exposed active sites. Scanning electrochemical microscopy (SECM) is an attractive method to determine the influence of defects on macroscopic performance metrics thanks to its ability to measure the relative rates of competing electrochemical reactions with high spatial resolution over the electrode. Here, we report the use of SECM to determine the influence of overlayer defects on the selectivity of silicon oxide (SiO

Seawater electrolysis offers significant logistical advantages over freshwater electrolysis but suffers from a fundamental selectivity problem at the anode. To prevent the evolution of toxic chlorine alongside the evolution of oxygen, a promising approach is the use of electrochemically inert overlayers. Such thin films can exert a perm-selective effect, allowing the transport of water and oxygen between the bulk electrolyte and the electrocatalytic buried interface while suppressing the transport of chloride ions. In this work, we investigate thin (5-20 nm) overlayer films composed of amorphous silicon oxide (SiOx) and their application to suppressing the chlorine evolution reaction (CER) in favor of the oxygen evolution reaction (OER) during acidic saltwater electrolysis on three different types of electrodes. While SiOx overlayers are seen to be an effective barrier against the CER on well-defined, smooth Pt thin films, decreasing the CER activity roughly 20-fold, this ability has not been previously explored on Ir-based catalysts with a higher surface area relevant to industrial applications. On amorphous iridium oxide electrodes, the selectivity toward the CER versus the OER was marginally reduced from similar to 98 to similar to 94%, which was attributed to the higher abundance of defects in overlayers deposited on the rougher electrode. On the other hand, Ir-based anodes consisting of thick mixed metal oxide films supported on Ti showed a significant decrease in CER selectivity, from similar to 100 to similar to 50%, although this came at the cost of reduced activity toward the OER. These results show that the morphology and composition of the underlying electrode play important roles in the effectiveness of the selective overlayers and provide guidance for further development of high-surface-area OER-selective anodes.

The development of new modes at x-ray free electron lasers has inspired novel methods for studying fluctuations at different energies and timescales. For closely spaced x-ray pulses that can be varied on ultrafast time scales, we have constructed a pair of advanced instruments to conduct studies targeting quantum materials. We first describe a prototype instrument built to test the proof-of-principle of resonant magnetic scattering using ultrafast pulse pairs. This is followed by a description of a new endstation, the so-called fluctuation–dissipation measurement instrument, which was used to carry out studies with a fast area detector. In addition, we describe various types of diagnostics for single-shot contrast measurements, which can be used to normalize data on a pulse-by-pulse basis and calibrate pulse amplitude ratios, both of which are important for the study of fluctuations in materials. Furthermore, we present some new results using the instrument that demonstrates access to higher momentum resolution.

This study describes and demonstrates key steps in a carbon-negative process for manufacturing cement from widely abundant seawater-derived magnesium (Mg) feedstocks. In contrast to conventional Portland cement, which starts with carbon-containing limestone as the source material, the proposed process uses membrane-free electrolyzers to facilitate the conversion of carbon-free magnesium ions (Mg 2+ ) in seawater into magnesium hydroxide [Mg(OH) 2 ] precursors for the production of Mg-based cement. After a low-temperature carbonation curing step converts Mg(OH) 2 into magnesium carbonates through reaction with carbon dioxide (CO 2 ), the resulting Mg-based binders can exhibit compressive strength comparable to that achieved by Portland cement after curing for only 2 days. Although the proposed “cement-from-seawater” process requires similar energy use per ton of cement as existing processes and is not currently suitable for use in conventional reinforced concrete, its potential to achieve a carbon-negative footprint makes it highly attractive to help decarbonize one of the most carbon-intensive industries.

Two preregistered experiments with 2,733 U.S. high school students (age range = 13-19 years) compared the impact of different messages on adolescents' motivation to control social media use (SMU). A traditional message emphasized the benefits of avoiding SMU, whereas a values-alignment message framed controlling SMU as being consistent with autonomy and social justice. Compared to no message or a traditional message, in both studies, a values-alignment message led to greater motivation to control SMU immediately afterward, and in Study 2, awareness of "addictive" social media designs 3 months later. As hypothesized, values-alignment messaging was more motivating for girls than boys. Results offer preliminary support for leveraging adolescents' drives for autonomy and social justice to motivate self-regulation of SMU.

RuO2 is a highly active electrocatalyst for the oxygen evolution reaction (OER) but is unstable in acidic environments. Herein we investigate the encapsulation of RuO2 nanoparticles with semipermeable, nanoscopic silicon oxide (SiOx) overlayers as a strategy to improve their stability. SiOx encapsulated RuO2 (SiOx|RuO2) electrodes were prepared by drop-casting RuO2 nanoparticles onto glassy carbon substrates followed by deposition of SiOx overlayers of varying thickness by a room temperature photochemical deposition process. The best-performing SiOx|RuO2 electrodes consisted of 2–3 nm thick SiOx overlayers on top of RuO2 particles and 3–7 nm thick SiOx on the glassy carbon substrate. Such electrodes exhibited lower overpotentials relative to bare RuO2 due to an improved electrochemically active surface area while also demonstrating an ability to retain OER activity over time, especially at higher overpotentials. Surprisingly, it was found that the SiOx coating was unable to prevent Ru dissolution, which was found to be proportional to the charge passed and independent of the presence or thickness of the SiOx coating. Thus, other possible explanations for the improved current retention of SiOx|RuO2 electrodes are discussed, including the influences of the overlayer on bubble dynamics and the stability of the underlying glassy carbon substrate.

Modifying an electrocatalyst surface by encapsulating it with a nanoscale oxide membrane is an attractive approach for improving its activity, stability, and selectivity. However, little is known a...

Background Diffuse gliomas display heterogeneous biology, natural history, response to treatments, and outcome. According to the 2021 WHO Classification, an integration of histological and molecular factors is needed for the diagnosis of diffuse gliomas. The Italian Association of Neuro-Oncology (AINO), with the participation of the Italian Society of Neurosurgery (SINch), promoted a survey to explore how the 2021 WHO molecular diagnostic criteria are integrated into clinical practice in a national framework. Material and Methods A web-based survey containing 38-item multiple-choice questions was sent to members of the AINO and SINch in February 2022 via the respective email listings of these organizations. Results We collected 152 answers. Most attendants were < 45-year-old (117, 77.0%). Participants from North, Centre and South of Italy were 85 (55.9%), 38 (25.0%), and 29 (19.1%). Academic and non-academic hospitals were 35 (46.1%) and 82 (53.9%). The presence of an institutional Brain Tumour Board was reported in 108 cases (71.7%). One hundred forty attendees (92.1%) reported that IDH mutation was assessed in all glioma patients regardless of age. The 1p19q-codeletion was assessed routinely in all IDH-mutant gliomas in 88 (57.9%) or when TP53 mutation and/or ATRX expression was found (45, 29.6%). The MGMTp methylation was assessed, regardless of grading, at diagnosis in 110 (72.4%), and at second surgery in 82 (53.9%). Eighty (52.6%) performed a quantitative analysis of MGMTp status. The CDKN2A/B homozygous deletion in IDH-mutant lower-grade astrocytomas was routinely investigated in 53 (34.9%). Assessment of EGFR amplification, pTERT status or +7/-10 chromosome alterations to stratify IDH-wildtype lower-grade astrocytomas was reported in 76 (50.0%), 43 (28.3%), and 16 (10.5%) cases. Rarer alterations were less commonly investigated (H3K27M: 34, 22.4%; H3G34: 11, 7.2%; BRAF: 18, 11.8%; NTRK: 16, 10.5%), being usually evaluated in selected cases (e.g., younger patients). Academic vs non-academic hospitals treated more patients per year (> 300 in 22/70, 31.4% vs 3/82, 3.7%, p Conclusion The availability of new molecular markers is increasing among Italian Neuro-Oncology Centres. However, there is still a gap with the proposed criteria of the 2021 WHO Classification and the real-life application. A critical issue remains how to select patients who might benefit from the identification of some extremely rare mutations in light of targeted therapies.

Background to analyze GBM recurrence pattern after standard chemoradiotherapy according to different target volume delineations. We hypothesized that reduced target volume margins may result in similar pattern of failure. Material and Methods 207 patients with GBM who recurred after standard chemoradiation were evaluated. According to the Advisory Committee for Radiation Oncology Practice (ACROP) committee of the European Organisation for Research and Treatment of Cancer (EORTC) target volume delineation guideline, the clinical target volume (CTV) used for treatment planning consisted of residual tumor and resection cavity plus 2-cm margin. MRI scans showing tumor recurrences were fused with the planning computed tomography (CT), and the patterns of failure were analyzed dosimetrically using dose-volume histograms. The recurrent lesions were defined as in-field, marginal, or distant if >80%, 20-80%, or Results The median overall survival and progression-free survival were 15.3 months and 7.8 months, respectively, from the date of surgery. Recurrences were in-field in 180 patients, marginal in 5 patients, and distant in 22 patients. Analysis of O6-methylguanine-DNA-methyltransferase (MGMT) promoter methylation status showed different recurrence patterns of GBMs in patients with MGMT methylated compared with patients with MGMT unmethylated status. Recurrences occurred in-field and distant in 75.6% and 18.6% of methylated patients and in 91.8% and 6% of unmethylated patients, respectively (p=0.0046). Patterns of failure were similar between the different treatment plans. Reduced target volumes were associated with significantly lower doses of 20-50 Gy to normal brain and hippocampi (p=0.0001). Conclusion Most of patients treated with standard chemioradiotherapy have in-field recurrences; however, an increased risk of distant recurrences occurs in methylated tumors. The use of target delineation using 1-cm CTV margin is associated with smaller volumes of normal brain and hippocampi irradiated to high doses, without significant changes in the pattern of failure. The impact of different target delineation in terms of efficacy and risk of late radiation-induced toxicity should be assessed prospectively.

Additive manufacturing encompasses an emerging class of techniques that are increasingly finding applications in the field of electrochemistry. While most of these demonstrations have involved the use of 3D-printing to fabricate structural components of electrochemical devices, this manuscript describes the design, manufacture and performance of 3D-printed porous flow-through electrodes employed in an electrolyzer that is itself made almost entirely by 3D-printing. These electrodes were 3D-printed using fused deposition modeling (FDM) from a composite of conductive carbon and polylactic acid (PLA), followed by electrodeposition of nickel (Ni) electrocatalyst. The stability and performance of these Ni-PLA electrodes were evaluated for water electrolysis in 1.0 M sodium hydroxide (NaOH). After characterizing the performance of a single electrode pair for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), three pairs of electrodes were incorporated into a simple and scalable 3D-printed membraneless electrolyzer by “clicking” them into a monolithic lid containing manifolding for collection of the O2 and H2 product gases. The device utilizes a membraneless architecture capable of operating in a stagnant electrolyte through buoyancy-driven separation of product gases, and allowing for easy regeneration of electrodes by electrodeposition. Device operation was evaluated through a combination of electroanalytical measurements, in situ high-speed video imaging, and finite element modeling. Although the efficiency and cross-over rates of these membraneless electrolyzers fall below what is required for commercial applications, additive manufacturing of electrodes offers an exciting new design space to improve performance and enable robust operation for applications where membrane-based electrolyzers are inherently unstable.

Emerging membraneless electrolyzers offer an attractive approach to lowering the cost of hydrogen (H2) production from water electrolysis thanks to potential advantages in durability and manufacturability that are made possible by elimination of membranes or diaphragms from the device architecture. However, a fair comparison of the performance limits of membraneless electrolyzers to conventional electrolyzers is hindered by the early stage of research and absence of established design rules for the former. This task is made all the more difficult by the need to quantitatively describe multiphase flow between the electrodes in membraneless electrolyzers, which can have a huge impact on gas product purity. Using a parallel plate membraneless electrolyzer (PPME) as a model system, this study takes a combined experimental and modeling approach to explore its performance limits and quantitatively describe the trade-offs between efficiency, current density, electrode size, and product purity. Central to this work is the use of in situ high-speed videography (HSV) to monitor the width of H2 bubble plumes produced downstream of parallel plate electrodes as a function of current density, electrode separation distance, and the Reynolds number (Re) associated with flowing 0.5 M H2SO4 electrolyte. These measurements reveal that the HSV-derived dimensionless bubble plume width serves as an excellent descriptor for correlating the aforementioned operating conditions with H2 crossover rates. These empirical relationships, combined with electrochemical engineering design principles, provide a valuable framework for exploring performance limits and guiding the design of optimized membraneless electrolyzers. Our analysis shows that the efficiencies and current densities of optimized PPMEs constrained to H2 crossover rates of 1% can exceed those of conventional alkaline electrolyzers but are lower than the efficiencies and current densities achieved by zero-gap polymer electrolyte membrane (PEM) electrolyzers.

A need for future research on ultrathin oxide layers that transcends many topics brought up in the outlook sections at the end of the individual chapters is a deeper understanding of the fundamental physical and chemical processes that occur within and at the interfaces of oxide layers. Improved knowledge of these processes is expected to be essential for guiding the design and selection of ultrathin oxides for both existing commercial technologies and novel applications. In this final chapter, major challenges for achieving these goals are outlined within the framework of modeling and experimental advances that are anticipated to be necessary to overcome them. First, challenges and opportunities related to modeling ultrathin oxides are discussed, followed by descriptions of emerging new spectroscopic techniques that are particularly well suited to probing buried oxide/semiconductor or oxide/metal interfaces. Lastly, this chapter highlights the importance of advancing experimental techniques capable of uncovering the dynamics of interfacial phenomena at ultrathin oxide layers that occur at timescales spanning many orders of magnitude.

Following a brief mention of the vital importance of thin oxide layers in the technological development of civilizations over millennia and their ubiquity in Nature, the significance of the advent of nanoscience that enabled the development of ultrathin layers for a wealth of energy-related applications over the past couple of decades is emphasized. Key chemical and physical properties of metal oxide nanolayers and their tunability are described, followed by brief introductions to individual chapters that highlight the connections between them.

This chapter describes the use of ultrathin oxide overlayers to modify and control the properties of electrocatalysts. Of particular interest are oxide-encapsulated electrocatalysts (OECs), for which the oxide overlayers are permeable to electroactive species such that electrochemical reactions occur at the buried interface between the overlayer and active electrocatalyst component. Such OECs offer several advantages over conventional electrocatalysts that are directly exposed to the electrolyte, presenting opportunities to improve the durability, selectivity, and activity of the active electrocatalyst material. However, the intertwined nature of the physical and chemical phenomena that underlie OEC operation adds complexity to the task of rationally designing OECs, and an improper choice of operating conditions or overlayer characteristics can be highly detrimental to their performance. To help researchers overcome these challenges, this chapter describes (i) the transport and kinetic principles that underlie OEC operation and (ii) experimental tools and methodologies that can be used to evaluate OEC performance. Collectively, the principles and methodologies described here can serve as a framework for developing design rules for optimized OECs that can be applied to a wide range of electrochemical energy applications.

The exploration of the universe has recently entered a new era thanks to the multimessenger paradigm, characterized by a continuous increase in the quantity and quality of experimental data that is obtained by the detection of the various cosmic messengers (photons, neutrinos, cosmic rays and gravitational waves) from numerous origins. They give us information about their sources in the universe and the properties of the intergalactic medium. Moreover, multi-messenger astronomy opens up the possibility to search for phenomenological signatures of quantum gravity. On the one hand, the most energetic events allow us to test our physical theories at energy regimes which are not directly accessible in accelerators; on the other hand, tiny effects in the propagation of very high energy particles could be amplified by cosmological distances. After decades of merely theoretical investigations, the possibility of obtaining phenomenological indications of Planck-scale effects is a revolutionary step in the quest for a quantum theory of gravity, but it requires cooperation between different communities of physicists (both theoretical and experimental). This review, prepared within the COST Action CA18108 ‘‘Quantum gravity phenomenology in the multi-messenger approach", is aimed at promoting this cooperation by giving a state-of-the art account of the interdisciplinary expertise that is needed in the effective search of quantum gravity footprints in the production, propagation and detection of cosmic messengers., Talent Scientific Research Program of College of Physics, Sichuan University 1082204112427, Fostering Program in Disciplines Possessing Novel Features for Natural Science of Sichuan University 2020SCUNL209, 1000 Talent program of Sichuan province 2021, Xunta de Galicia, European Commission European Union ERDF, "Maria de Maeztu'' Units of Excellence program MDM-2016-0692, Red Tematica Nacional de Astroparticulas RED2018-102661-T, La Caixa Foundation 100010434, European Commission 847648 LCF/BQ/PI21/11830030 754510, Ministry of Education, Science & Technological Development, Serbia 451-03-9/2021-14/200124, FSR Incoming Postdoctoral Fellowship Ministry of Education, Science and Technological Development, Serbia 451-03-9/2021-14/200124, University of Rijeka grant uniri-prirod-18-48, Croatian Science Foundation (HRZZ) IP-2016-06-9782, Villum Fonden 29405 DGA-FSE 2020-E2117R, European Regional Development Fund through the Center of Excellence (TK133) "The Dark Side of the Universe'' European Regional Development Fund (ESIF/ERDF), Ministry of Education, Youth & Sports - Czech Republic CoGraDS-CZ.02.1.01/0.0/0.0/15 003/0000437, Blavatnik grant, Basque Government IT-97916 Basque Foundation for Science (IKERBASQUE), European Space Agency C4000120711 4000132310, FNRS (Belgian Fund for Research), Programa de Apoyo a Proyectos de Investigacion e Innovacion Tecnologica (PAPIIT), Universidad Nacional Autonoma de Mexico TA100122, National University of La Plata X909 DICYT 042131GR, National Research, Development & Innovation Office (NRDIO) - Hungary 123996, FQXi, Swiss National Science Foundation (SNSF), European Commission 181461 199307, Netherlands Organization for Scientific Research (NWO) 680-91-119 15MV71, Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT) Japan Society for the Promotion of Science, Grants-in-Aid for Scientific Research (KAKENHI) 20H01899 20H05853 JP21F21789, Estonian Research Council PRG356, Julian Schwinger Foundation, Generalitat Valenciana Excellence PROMETEO-II/2017/033 PROMETEO/2018/165, Istituto Nazionale di Fisica Nucleare (INFN), European ITN project HIDDeN H2020-MSCA-ITN-2019//860881-HIDDeN, Swedish Research Council, European Commission 2016-05996 European Research Council (ERC) European Commission 668679, Advanced ERC grant TReX, Ministry of Education, Universities and Research (MIUR) 2017X7X85K, Fonds de la Recherche Scientifique - FNRS 4.4501.18, Ministry of Research, Innovation and Digitization - Romania PN19-030102-INCDFM PN-III-P4ID-PCE-2020-2374, United States Department of Energy (DOE) DE-SC0020262, Ministry of Science, ICT & Future Planning, Republic of Korea 075-15-2020-778, German Academic Scholarship Foundation German Research Foundation (DFG) 408049454 420243324 425333893 445990517 Germany's Excellence Strategy (EXC 2121 "Quantum Universe'') 390833306 390837967 Federal Ministry of Education & Research (BMBF) 05 A20GU2 05 A20PX1, Centro de Excelencia "Severo Ochoa'' SEV-2016-0588, CERCA program of the Generalitat de Catalunya, Agencia de Gestio D'Ajuts Universitaris de Recerca Agaur (AGAUR) Generalitat de Catalunya 2017-SGR-1469 2017-SGR-929 ICCUB CEX2019-000918-M, National Science Centre, Poland 2019/33/B/ST2/00050 2017/27/B/ST2/01902, Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPQ) 306414/2020-1, Dicyt-USACH 041931MF, National Science Fund of Bulgaria KP-06-N 38/11 RCN ROMFORSK 302640, Comunidad de Madrid 2018-T1/TIC-10431 2019-T1/TIC-13177 S2018/NMT-4291, UK Research & Innovation (UKRI), Science & Technology Facilities Council (STFC) ST/T000759/1 ST/P000258/1 ST/T000732/1 ST/V005596/1, Portuguese Foundation for Science and Technology UIDB/00618/2020 UIDB/00777/2020 UIDP/00777/2020 CERN/FIS-PAR/0004/2019 PTDC/FIS-PAR/29436/2017 PTDC/FISPAR/31938/2017 PTDC/FIS-OUT/29048/2017 SFRH/BD/137127/2018, Centre National de la Recherche Scientifique (CNRS), LabEx UnivEarthS ANR-10-LABX-0023 ANR18-IDEX-0001, Junta de Andalucia European Commission A-FQM-053-UGR18, Natural Sciences and Engineering Research Council of Canada (NSERC) RGPIN-2021-03644, National Science Centre Poland Sonata Bis 2019/33/B/ST2/00050 DEC-2017/26/E/ST2/00763, Natural Sciences and Engineering Research Council of Canada (NSERC) DGIID-DGA 2015-E24/2, Spanish Research State Agency and Ministerio de Ciencia e Innovacion MCIN/AEI PID2019-104114RB-C32 PID2019-105544GB-I00 PID2019-105614GB-C21 PID2019106515GB-I00 PID2019-106802GB-I00 PID2019-107394GB-I00 PID2019-107844GB-C21 PID2019-107847RB-C41 MCIN/AEI PGC2018-095328-B-I00 PGC2018-094856-B-I00 PGC2018-096663-B-C41 PGC2018-096663-B-C44 PGC2018-094626-BC21 PGC2018-101858-B-I00 FPA2017-84543-P FPA2016-76005-C2-1-P, Spanish 'Ministerio de Universidades' BG20/00228 Spanish Government PID2020-115845GBI00 Generalitat de Catalunya Comunidad de Madrid S2018/NMT-4291 Spanish Government PID2019-105544GB-I00, Perimeter Institute for Theoretical Physics, Government of Canada through the Department of Innovation, Science and Economic Development, Province of Ontario through the Ministry of Colleges and Universities, Centre National de la Recherche Scientifique (CNRS), Netherlands Organization for Scientific Research (NWO), Fundamental Questions Institute (FQXi), European Cooperation in Science and Technology (COST) CA18108, Research Council of University of Guilan, Iniziativa Specifica TEONGRAV Iniziativa Specifica QGSKY Iniziativa Specifica QUAGRAP Iniziativa Specifica GeoSymQFT, the Spanish Research State Agency and Ministerio de Ciencia e Innovacion MCIN/AEI PID2020-115845GBI00 PID2019-108485GB-I00 PID2020-113334GB-I00 PID2020-113701GB-I00 PID2020-113775GB-I00 PID2020-118159GB-C41 PID2020-118159GA-C42 PRE2019-089024, Rothchild grant UID/MAT/00212/2020 FPU18/04571

Previous studies on scanning electrochemical microscopy (SECM) imaging with nonlocal continuous line probes (CLPs) have demonstrated the ability to increase areal imaging rates by an order of magnitude compared to SECM based on conventional ultramicroelectrode (UME) disk electrodes. Increasing the linear scan speed of the CLP during imaging presents an opportunity to increase imaging rates even further but results in a significant deterioration in image quality due to transport processes in the liquid electrolyte. Here, we show that compressed sensing (CS) postprocessing can be successfully applied to CLP-based SECM measurements to reconstruct images with minimal distortion at probe scan rates greatly exceeding the conventional SECM ″speed limit″. By systematically evaluating the image quality of images generated by adaptable postprocessing CS methods for CLP-SECM data collected at varying scan rates, this work establishes a new upper bound for CLP scan rates. While conventional SECM imaging typically uses probe scan speeds characterized by Peclet numbers (Pe) < 1, this study shows that CS postprocessing methods can allow for an accurate image reconstruction for Pe approaching 5, corresponding to an order of magnitude increase in the maximum probe scan speed. This upper limit corresponds to the onset of chaotic convective flows within the electrolyte for the probes investigated in this work, highlighting the importance of considering hydrodynamics in the design of fast-scanning probes.

The world’s growing demand for fresh water is creating increasing stress on existing fresh water sources and environmental hazards related to the generation of high salinity reject brine streams that are produced during seawater desalination. Electrochemical separations technologies offer attractive sources to treat brines to reduce brine salinity and/or harvest valuable chemicals or materials from dissolved species present in the brine. In this work, our team has explored the use of membrane-free electrochemical electrolyzers for treatment and separation processes through their ability to create large pH differentials between anode and cathode effluent streams. Because these devices do not contain membranes, they are attractive for operating in the harsh brine environment, which contains many impurities that can result in membrane scaling or fouling. In the first part of this talk, I will describe the basic operating principles of these electrolyzers, which rely on the use of flow-induced separation of anode and cathode effluent streams to create large pH gradients. During operation, it is generally desirable to maximize pH differentials by choosing flow conditions that limit cross-over of product species, thus ensuring high current utilization, while avoiding unnecessary dilution of H+ and OH- within the product streams. This trade-off between cross-over and dilution was studied for porous flow-through electrodes, where we systematically explore the combined influences of volumetric flow rates, catalyst placement, and operating current densities on the pH differential generated by electrolyzers fed with pH neutral brine solutions. Aided by the use of in situ high speed videography and colorimetric imaging of pH differentials, these experiments show that the Damköhler number is an excellent descriptor that can be used to identify the optimal operating conditions that maximize pH differential. Further, we show that the in-plane distribution of active catalyst loading on the porous electrode support has a large impact on the maximum pH differential that can be achieved. Finally, this presentation will also describe the tolerance of electrode durability to the presence of dissolved alkaline earth metal ions such as Mg2+, which can deposit on cathodes and result in scaling if not properly managed.

The U.S. Department of Energy recently announced its first Energy Earthshot on Clean Hydrogen, with a cost target of $1/kg-H2 by 2031. Assuming future utility-scale grid electricity prices from photovoltaics ($0.02/kWh), 80% of the cost of H2 would come from performing low-temperature water electrolysis at its thermoneutral voltage, with zero additional overpotential. This fact motivates alternative, less-expensive means of using light to generate mobile charge carriers than photovoltaics, and reactor designs with exceedingly low capital costs, like those we recently invented. Systems using low capital cost reactors benefit from low-voltage operation, which represents a paradigm shift from current state-of-the-art electrolyzers that aim to operate at high current densities. Analytical models predict that solar photocatalytic water splitting inherently operates at low voltages through use of an ensemble of optically thin photoabsorbers each operating at a low rate. Collectively the ensemble exhibits larger overall solar-to-hydrogen conversion efficiencies in comparison to optically thick designs. In efforts to attain these predicted higher efficiencies, we are performing detailed studies on the properties of state-of-the-art doped SrTiO3 and BiVO4 photocatalyst particles. During my talk, I will share our recent efforts in atomic-layer deposited ultrathin oxide coatings to impart redox selectivity and materials stability, single-photocatalyst-particle current–potential behavior and mobile charge carrier properties, and atomic-level information on dopant distributions and materials interfaces obtained from electron microscopies and X-ray spectroscopies. Collectively, our discoveries provide new design guidelines and additional research pathways for the development of effective composite materials to serve as active components in techno-economically viable artificial photosynthetic devices.

(Bi)carbonate electrolysis offers an attractive opportunity for integrated carbon dioxide (CO2) capture and conversion whereby a carbonate-laden aqueous capture solution can be directly fed to an electrolyzer before being recycled to the CO2 capture unit(s). Among the previous studies that have demonstrated the viability of (bi)carbonate electrolysis, bipolar membranes are commonly used to deliver protons to the cathode where they convert (bi)carbonate into CO2 that is subsequently reduced at the cathode. However, these membranes can be susceptible to fouling or degradation, which may lead to device failure. Here, we present a scalable and potentially low-cost packed bed membraneless electrolyzer (PBME) concept for the conversion of bicarbonate into CO based on train of porous flow-through electrodes. At the anode, hydrogen oxidation reaction is used to produce protons, which rapidly react with bicarbonate to generate CO2 for electrochemical CO2 reduction at the downstream cathode in this membrane-free electrolyzer design. This study highlights the ability of the PBME design to minimize the magnitude of pH swings within the electrolyzer and enable high CO2 utilization rates. Tests of multi-cell PBMEs show enhanced performance compared to single-cell PBMEs and demonstrate the scalability of this PBME design.

Similar to natural photosynthesis, Z-scheme photocatalytic water splitting relies on two different light absorbing components that are coupled by a redox active mediator that shuttles charge between them. Such a two-absorber system possesses several advantages over single absorber photocatalytic system, including higher theoretical solar-to-hydrogen conversion efficiency, relaxed band alignment requirements, and the potential for inherently safe operation whereby H2 and O2 evolution occur in separated compartments. However, a major disadvantage and challenge for Z-scheme photocatalysis is that the presence of a redox mediator introduces two undesirable back-reactions on top of parasitic H2 oxidation and O2 reduction reactions that can occur in a single absorber photocatalytic system. Previous research efforts have identified the use of semi-permeable oxide coatings as an attractive approach to suppress these thermodynamically favored redox reactions while still permitting the desired water splitting and mediator redox reactions to occur. Here, we present a combined experimental and computational approach based on model thin films that is used to (i) probe the performance limits of oxide-encapsulated photocatalysts, (ii) quantify the effects of coating defects on performance, and (iii) guide the rational design of coatings aimed at maximizing the solar-to-hydrogen conversion efficiency of a target photocatalytic system. This work specifically focusses on the development of silicon and titanium oxide coatings for Z-scheme water splitting based on a Fe(II)/Fe(III) mediator, showing that the best coatings can achieve selectivities > 90 % towards the H2 and O2 evolution reactions over undesired Fe(II)/Fe(III) back reactions. Another key finding from this work is that coating defects can have a significant influence on the performance of encapsulated electrodes, as revealed by scanning electrochemical microscopy (SECM) measurements that were used to locally quantify the parasitic back reaction rates around individual defects to determine their impact on the global selectivity of an encapsulated electrode.

Z-scheme semiconductor particles present in an aqueous solution with soluble redox shuttles provides a promising two-step approach to split water to produce hydrogen and oxygen using sunglight. This approach facilitates efficient utilization of the incident solar spectrum with tandem light-absorbers and promotes safe reactor operation with hydrogen and oxygen produced in physically distinct locations. Thermodynamically, these systems are projected to achieve solar-to-hydrogen (STH) efficiencies that are comparable to the electrode architectures, which are as large as 34% with idealized light absorbers and perfect reaction selectivity1. Up to 4% STH efficiencies were theoretically projected for state-of-the-art light absorbers and cocatalysts with diffusion-driven redox shuttle transport between reaction sites2. However, practical demonstrations are limited to efficiencies that are significantly smaller (less than 1%)3. Two main factors impeding actual performance in these systems include: (a) undesired reactions of any redox species, including hydrogen, oxygen, or the redox shuttle species, on the photocatalyst site; and (b) mass-transfer limitations of reactant/product species between oxygen and hydrogen evolution reaction sites. In this work, I will present materials- and device-level insights obtained from physics-based models of varying complexities. An expanded, zero-dimensional (0-D), equivalent-circuit model is developed to probe the effectiveness of semipermeable oxide coatings to achieve reaction selectivity. This model introduces powerful innovations to model parallel/competing redox reactions at the valence and conduction bands, while also accounting for mass-transfer limitations. Moreover, our framework provides a tractable approach to quantify the multidimensional dependencies of coating transport and kinetic parameters, concentration of light absorbers, and species mass-transfer rates on the STH efficiencies. At the reactor-scale, we assess the viability of natural convective currents to enhance species mixing. Temperature and concentration profiles are predicted from a two-dimensional (2-D), coupled flow, heat, and mass-transfer model of two reaction compartments separated by a membrane. Modeling predictions are compared to and validated against experimental measurements on dual-compartment reactor prototypes. Enhanced rate of species transport is predicted in the presence of thermal convection in addition to diffusion. Improved species mixing is observed for the horizontal, as compared to the vertically stacked, arrangement of reaction compartments, and is attributed to attenuation of incident sunlight by the membrane present along the optical path. With 2-cm tall reaction compartments, the minimum redox shuttle concentration needed to sustain a 10% STH efficiency decreases by 80% in the presence of natural convection as compared to diffusion. Overall, these results provide new insights and strategies to realize highly effective materials-to-device scale designs for Z-scheme photocatalytic solar fuel reactors with soluble redox shuttles. References (1) Keene, S.; Bala Chandran, R.; Ardo, S. Calculations of Theoretical Efficiencies for Electrochemically-Mediated Tandem Solar Water Splitting as a Function of Bandgap Energies and Redox Shuttle Potential. Energy Environ. Sci. 2019, 12 (1), 261–272. https://doi.org/10.1039/C8EE01828F. (2) Bala Chandran, R.; Breen, S.; Shao, Y.; Ardo, S.; Weber, A. Z. Evaluating Particle-Suspension Reactor Designs for Z-Scheme Solar Water Splitting via Transport and Kinetic Modeling. Energy Environ. Sci. 2018, 11 (1), 115–135. https://doi.org/10.1039/C7EE01360D. (3) Wang, Z.; Hisatomi, T.; Li, R.; Sayama, K.; Liu, G.; Domen, K.; Li, C.; Wang, L. Efficiency Accreditation and Testing Protocols for Particulate Photocatalysts toward Solar Fuel Production. Joule 2021, 5 (2), 344–359. https://doi.org/10.1016/j.joule.2021.01.001.

According to density functional theory, monolayer (ML) MoS2 is predicted to possess electrocatalytic activity for the hydrogen evolution reaction (HER) that approaches that of platinum. However, its observed HER activity is much lower, which is widely believed to result from a large Schottky barrier between ML MoS2 and its electrical contact. In order to better understand the role of contact resistance in limiting the performance of ML MoS2 HER electrocatalysts, this study has employed well-defined test platforms that allow for the simultaneous measurement of contact resistance and electrocatalytic activity toward the HER during electrochemical testing. At open circuit potential, these measurements reveal that a 0.5 M H2SO4 electrolyte can act as a strong p-dopant that depletes free electrons in MoS2 and leads to extremely high contact resistance, even if the contact resistance of the as-made device in air is originally very low. However, under applied negative potentials this doping is mitigated by a strong electrolyte-mediated gating effect which can reduce the contact and sheet resistances of properly configured ML MoS2 electrocatalysts by more than 5 orders of magnitude. At potentials relevant to HER, the contact resistance becomes negligible and the performance of MoS2 electrodes is limited by HER kinetics. These findings have important implications for the design of low-dimensional semiconducting electrocatalysts and photocatalysts.

The performance of direct alcohol fuel cells (DAFCs) is frequently constrained by the efficiencies of the electrocatalysts used for the necessary alcohol oxidation reactions (AORs), which require high overpotentials to remove poisoning CO intermediates from the catalyst surface. Silicon Oxide (SiOx) encapsulated Pt electrodes have previously been shown to reduce the potential required to remove CO, and greatly enhance the activity of Pt-based catalysts for alcohol oxidation. To better understand the mechanism of this enhancement, silicon oxide layers with varying concentrations of residual carbon were employed to probe the compositional effects of overlayer composition on AORs. Overall, it was found that carbon-free, SiOx encapsulated samples exhibited the largest reduction in CO oxidation potential, with carbon rich samples still demonstrating a slight decrease in required potential compared to unencapsulated, bare Pt. Surprisingly, samples that demonstrated the largest reductions in CO oxidation potentials did not show the highest activity enhancement for alcohol oxidation. Instead, samples that had the highest concentration of carbon showed the highest degree of current enhancement for formic acid, methanol, and ethanol oxidation. For larger alcohols like propanol and butanol, the measured activity for alcohol oxidation on encapsulated samples began to diminish, credited to the additional mass transport resistance that the overlayer introduces. These observations offer insights into how the composition and properties of SiOx overlayers can affect the reactivity and transport of species in an electrochemical system, and offer an additional level of design for the development of future electrocatalyst architectures.