A solar-to-chemical conversion efficiency up to 0.26% achieved in ambient conditions.

Artificial photosynthesis in ambient conditions is much less efficient than the solar-to-biomass conversion (SBC) processes in nature. Here, we successfully mimic the NADP-mediated photosynthetic processes in green plants by introducing redox moieties as the electron acceptors in the present conjugated polymeric photocatalyst. The current artificial process substantially promotes the charge carrier separation efficiency and the oxygen reduction efficiency, achieving a photosynthesis rate for converting Earth-abundant water and oxygen in air into hydrogen peroxide as high as 909 µmol⋅g-1⋅h-1 and a solar-to-chemical conversion (SCC) efficiency up to 0.26%. The SCC efficiency is more than two times higher than the average SBC efficiency in nature (0.1%) and the highest value under ambient conditions. This study presents a strategy for efficient SCC in the future.

Pyrogenic Black Carbon Suppresses Microbial Methane Production by Serving as a Terminal Electron Acceptor.

Methane (CH4) is the second most important greenhouse gas, 27 times as potent as CO2 and responsible for >30% of the current anthropogenic warming. Globally, more than half of CH4 is produced microbially through methanogenesis. Pyrogenic black carbon possesses a considerable electron storage capacity (ESC) and can be an electron donor or acceptor for abiotic and microbial redox transformation. Using wood-derived biochar as a model black carbon, we demonstrated that air-oxidized black carbon served as an electron acceptor to support anaerobic oxidation of organic substrates, thereby suppressing CH4 production. Black carbon-respiring bacteria were immediately active and outcompeted methanogens. Significant CH4 did not form until the bioavailable electron-accepting capacity of the biochar was exhausted. An experiment with labeled acetate (13CH3COO-) yielded 1:1 13CH4 and 12CO2 without biochar and predominantly 13CO2 with biochar, indicating that biochar enabled anaerobic acetate oxidation at the expense of methanogenesis. Methanogens were enriched following acetate fermentation but only in the absence of biochar. The electron balance shows that approximately half (∼2.4 mmol/g) of biochar's ESC was utilized by the culture, corresponding to the portion of the ESC > +0.173 V (vs SHE). These results provide a mechanistic basis for quantifying the climate impact of black carbon and developing ESC-based applications to reduce CH4 emissions from biogenic sources.

The CdIn2 S4 /WO3 Nanosheet Composite Has a Significantly Enhanced Photo-electrochemical Cathodic Protection Performance and Excellent Electron Storage Capability.

Photo-electrochemical cathodic protection (CP) technology is considered to be a green metallic corrosion protection technology that uses solar energy to protect from corrosion and does not consume any anode materials. In this work, a CdIn2 S4 /WO3 nanocomposite photoelectrode was prepared, and its photo-electrochemical CP performance and mechanism were studied and analyzed. WO3 has a well band matching with CdIn2 S4 , leading to a significantly enhanced photo-electrochemical CP performance of the nanocomposite. Meanwhile, as confirmed in this work, the CdIn2 S4 /WO3 nanocomposite can store photoinduced electrons under light illumination through intercalation reactions and changing the valence state of tungsten. Moreover, it can discharge in the dark state to provide continuous CP for the coupled metals. This research will promote the practical application process of the photo-electrochemical CP technology.

C-H Arylation of Benzene with Aryl Halides using H2 and a Water-Soluble Rh-Based Electron Storage Catalyst.

This paper reports the first example of C-H arylation of benzene under mild conditions, using H2 as an electron source {turnover numbers (TONs)=0.7-2.0 for 24 h}. The reaction depends on a Rh-based electron storage catalyst, and proceeds at room temperature and in aqueous solution. Furthermore, the H2 is inactive during the radical transfer step, greatly reducing unwanted side reactions.

Radical Stabilization of a Tripyridinium-Triazine Molecule Enables Reversible Storage of Multiple Electrons.

A novel organic molecule, 2,4,6-tris[1-(trimethylamonium)propyl-4-pyridiniumyl]-1,3,5-triazine hexachloride, was developed as a reversible six-electron storage electrolyte for use in an aqueous redox flow battery (ARFB). Physicochemical characterization reveals that the molecule evolves from a radical to a biradical and finally to a quinoid structure upon accepting four electrons. Both the diffusion coefficient and the rate constant were sufficiently high to run a flow battery with low concentration and kinetics polarization losses. In a demonstration unit, the assembled flow battery affords a high specific capacity of 33.0 Ah L-1 and a peak power density of 273 mW cm-2 . This work highlights the rational design of electroactive organics that can manipulate multi-electron transfer in a reversible way, which will pave the way to development of energy-dense, manageable and low-cost ARFBs.

An Iterative Divergent Approach to Conjugated Starburst Borane Dendrimers.

Using a new divergent approach, conjugated triarylborane dendrimers were synthesized up to the 2nd generation. The synthetic strategy consists of three steps: 1) functionalization, via iridium catalyzed C-H borylation; 2) activation, via fluorination of the generated boronate ester with K[HF2 ] or [N(nBu4 )][HF2 ]; and 3) expansion, via reaction of the trifluoroborate salts with aryl Grignard reagents. The concept was also shown to be viable for a convergent approach. All but one of the conjugated borane dendrimers exhibit multiple, distinct and reversible reduction potentials, making them potentially interesting materials for applications in molecular accumulators. Based on their photophysical properties, the 1st generation dendrimers exhibit good conjugation over the whole system. However, the conjugation does not increase further upon expansion to the 2nd generation, but the molar extinction coefficients increase linearly with the number of triarylborane subunits, suggesting a potential application as photonic antennas.

Electron Storage Capability and Singlet Oxygen Productivity of a RuII Photosensitizer Containing a Fused Naphthaloylenebenzene Moiety at the 1,10-Phenanthroline Ligand.

As a novel rylene type dye a diimine ligand with a fully rigid and extended π-system in its backbone was prepared by directly fusing a 1,10-phenanthroline building block with 1,8-naphthalimide. The corresponding heteroleptic ruthenium photosensitizer bearing one biipo and two tbbpy ligands was synthesized and extensively analyzed by a combination of NMR, single crystal X-ray diffraction, steady-state absorption and emission, time-resolved spectroscopy and different electrochemical measurements supported by time-dependent density functional theory calculations. The cyclic and differential pulse voltammograms revealed, that the naphthaloylenebenzene moiety enables an additional second reduction of the ligand. Moreover, this ligand possesses a very broad absorption in the visible region. In the RuII complex this causes an overlap of ligand-centered and metal-to-ligand charge transfer transitions. The emission of the complex is clearly redshifted compared to the ligand emission with very long-lived excited states lifetimes of 1.7 and 24.7 µs in oxygen-free acetonitrile solution. This behavior is accompanied by a surprisingly high oxygen sensitivity. Finally, this photosensitizer was successfully applied for the effective evolution of singlet oxygen challenging some of the common RuII prototype complexes.

SLS-2 - the upgrade of the Swiss Light Source.

An upgrade of the Swiss Light Source (SLS) is planned for 2021-2024 and includes the exchange of the existing storage ring by a new one providing about 40-50 times lower emittance in user operation mode. This will extend the performance of SLS in particular in the fields of coherent imaging, full-field tomography, soft X-ray angle-resolved photoelectron spectroscopy and resonant inelastic X-ray scattering. A science case and a conceptual design for the machine have been established. As a summary of these reports, the novel lattice design, undulator developments and scientific highlights are presented.

Hydrogen-Generating Ru/Pt Bimetallic Photocatalysts Based on Phenyl-Phenanthroline Peripheral Ligands.

Recent studies on hydrogen-generating supramolecular bimetallic photocatalysts indicate a more important role of the peripheral ligands than expected, motivating us to design a Ru/Pt complex with 4,7-diphenyl-1,10-phenanthroline peripheral ligands. Photoinduced intra- and inter-ligand internal conversion processes have been investigated using transient absorption spectroscopy, spanning the femto- to nanosecond timescale. After photoexcitation and ultrafast intersystem crossing, triplet states localised on either the peripheral ligands or on the bridging ligand/catalytic unit are populated in a non-equilibrated way. Time-resolved photoluminescence demonstrates that the lifetime for the Ru/Pt dinuclear species (795±8 ns) is significantly less than that of the mononuclear analogue (1375±20 ns). The photocatalytic studies show modest hydrogen turnover numbers, which is possibly caused by the absence of an excited state equilibrium. Finally, we identify challenges that must be overcome to further develop this class of photocatalysts and propose directions for future research.

Tris(2,2'-bipyridine)ruthenium Derivatives with Multiple Viologen Acceptors: Quadratic Dependence of Photocatalytic H2 Evolution Rate on the Local Concentration of the Acceptor Site.

Three Ru(bpy)3 (2+) derivatives tethered to multiple viologen acceptors, [Ru(bpy)2 (4,4'-MV2)](6+) , [Ru(bpy)2 (4,4'-MV4)](10+) , and [Ru(bpy)(4,4'-MV4)2 ](18+) [bpy=2,2'-bipyridine, 4,4'-MV2=4-ethoxycarbonyl-4'-(N-G1 -carbamoyl)-2,2'-bipyridine, and 4,4'-MV4=4,4'-bis(N-G1 -carbamoyl)-2,2'-bipyridine, where G1 =Asp(NHG2 )-NHG2 and G2 =-(CH2 )2 -N(+) C5 H4 -C5 H4 N(+) -CH3 ] were prepared as "photo-charge separators (PCSs)". Photoirradiation of these complexes in the presence of a sacrificial electron donor (EDTA) results in storage of electrons per PCS values of 1.3, 2.7, and 4.6, respectively. Their applications in the photochemical H2 evolution from water in the presence of a colloidal Pt H2 -evolving catalyst were investigated, and are discussed along with those reported for [Ru(bpy)2 (5,5'-MV4)](10+) , [Ru(4,4'-MV4)3 ](26+) , and [Ru(5,5'-MV4)3 ](26+) (Inorg. Chem. Front. 2016, 3, 671-680). The PCSs with high dimerization constants (Kd =10(5) -10(6) m(-1) ) are superior in driving H2 evolution at pH 5.0, whereas those with lower Kd values (10(3) -10(4) m(-1) ) are superior at pH 7.0, where Kd =[(MV(+) )2 ]/[MV(+) (.) ](2) . The (MV(+) )2 site can drive H2 evolution only at pH 5.0 as a result of its 0.15 eV lower driving force for H2 evolution relative to MV(+) (.) , whereas the PCSs with lower Kd values exhibit higher performance at pH 7.0 owing to the higher population of free MV(+) (.) . Importantly, the rate of electron charging over the PCSs is linear to the apparent H2 evolution rate, and shows an intriguing quadratic dependence on the number of MV(2+) units per PCS.

Decoupled Solar Energy Storage and Dark Photocatalysis in a 3D Metal-Organic Framework.

Materials enabling solar energy conversion and long-term storage for readily available electrical and chemical energy are key for off-grid energy distribution. Herein, the specific confinement of a rhenium coordination complex in a metal-organic framework (MOF) unlocks a unique electron accumulating property under visible-light irradiation. About 15 C gMOF -1 of electric charges can be concentrated and stored for over four weeks without loss. Decoupled, on-demand discharge for electrochemical reactions and H2 evolution catalysis is shown and light-driven recharging can be conducted for >10 cycles with ≈90% of the initial charging capacity retained. Experimental investigations and theoretical calculations link electron trapping to MOF-induced geometry constraints as well as the coordination environment of the Re-center, highlighting the key role of MOF confinement on molecular guests. This study serves as the seminal report on 3D porous colloids achieving photoaccumulation of long-lived electrons, unlocking dark photocatalysis, and a path toward solar capacitor and solar battery systems.

Starvation combined with constant anode potential triggers intracellular electron storage in electro-active biofilms.

The accumulation of electrons in the form of Extracellular Polymeric Substances (EPS) and poly-hydroxyalkanoates (PHA) has been studied in anaerobic processes by adjusting the access of microorganisms to the electron donor and final electron acceptor. In Bio-electrochemical systems (BESs), intermittent anode potential regimes have also recently been used to study electron storage in anodic electro-active biofilms (EABfs), but the effect of electron donor feeding mode on electron storage has not been explored. Therefore, in this study, the accumulation of electrons in the form of EPS and PHA was studied as a function of the operating conditions. EABfs were grown under both constant and intermittent anode potential regimes and fed with acetate (electron donor) continuously or in batch. Confocal Laser Scanning Microscopy (CLSM) and Fourier-Transform Infrared Spectroscopy (FTIR) were used to assess electron storage. The range of Coulombic efficiencies, from 25 to 82%, and the biomass yields, between 10 and 20%, indicate that storage could have been an alternative electron consuming process. From image processing, a 0.92 pixel ratio of poly-hydroxybutyrate (PHB) and amount of cells was found in the batch fed EABf grown under a constant anode potential. This storage was linked to the presence of living Geobacter and shows that energy gain and carbon source starvation were the triggers for intracellular electron storage. The highest EPS content (extracellular storage) was observed in the continuously fed EABf under an intermittent anode potential, showing that constant access to electron donor and intermittent access to the electron acceptor leads to the formation of EPS from the excess energy gained. Tailoring operating conditions can thus steer the microbial community and result in a trained EABf to perform a desired biological conversion, which can be beneficial for a more efficient and optimized BES.

Sulfonate-Based Triazine Multiple-Electron Anolyte for Aqueous Organic Flow Batteries.

A new highly soluble triazine derivative (SPr)34TpyTz showing three reversible redox processes with fast kinetics and high diffusion coefficients has been synthesized using an efficient, low-cost, and straightforward synthetic route. Concentrated single cell tests and DFT studies reveal a tendency of the reduced triazine species to form aggregates which could be avoided by tuning the supporting electrolyte concentration. Under the right conditions, (SPr)34TpyTz shows no capacity decay and good Coulombic, voltage, and energy efficiencies for the storage of two electrons. The storage of further electrons leads to a higher capacity decay and an increase of the electrolyte pH, suggesting the irreversible protonation of the generated species. So, a plausible mechanism has been proposed. A higher concentration of (SPr)34TpyTz shows slightly higher capacity decay and lower efficiencies due to the aggregate formation.

The effect of intermittent anode potential regimes on the morphology and extracellular matrix composition of electro-active bacteria.

Electro-active bacteria (EAB) can form biofilms on an anode (so-called bioanodes), and use the electrode as electron acceptor for oxidation of organics in wastewater. So far, bioanodes have mainly been investigated under a continuous anode potential, but intermittent anode potential has resulted in higher currents and different biofilm morphologies. However, little is known about how intermittent potential influences the electron balance in the anode compartment. In this study, we investigated electron balances of bioanodes at intermittent anode potential regimes. We used a transparent non-capacitive electrode that also allowed for in-situ quantification of the EAB using optical coherence tomography (OCT). We observed comparable current densities between continuous and intermittent bioanodes, and stored charge was similar for all the applied intermittent times (5 mC). Electron balances were further investigated by quantifying Extracellular Polymeric Substances (EPS), by analyzing the elemental composition of biomass, and by quantifying biofilm and planktonic cells. For all tested conditions, a charge balance of the anode compartment showed that more electrons were diverted to planktonic cells than biofilm. Besides, 27-43% of the total charge was detected as soluble EPS in intermittent bioanodes, whereas only 15% was found as soluble EPS in continuous bioanodes. The amount of proteins in the EPS of biofilms was higher for intermittent operated bioanodes (0.21 mg COD proteins mg COD biofilm-1) than for continuous operated bioanodes (0.05 mg COD proteins mg COD biofilm-1). OCT revealed patchy morphologies for biofilms under intermittent anode potential. Overall, this study helped understanding that the use of a non-capacitive electrode and intermittent anode potential deviated electrons to other processes other than electric current at the electrode by identifying electron sinks in the anolyte and quantifying the accumulation of electrons in the form of EPS.

Electron Storage in Electroactive Biofilms.

Microbial electrochemical technologies (METs) are promising for sustainable applications. Recently, electron storage during intermittent operation of electroactive biofilms (EABs) has been shown to play an important role in power output and electron efficiencies. Insights into electron storage mechanisms, and the conditions under which these occur, are essential to improve microbial electrochemical conversions and to optimize biotechnological processes. Here, we discuss the two main mechanisms for electron storage in EABs: storage in the form of reduced redox active components in the electron transport chain and in the form of polymers. We review electron storage in EABs and in other microorganisms and will discuss how the mechanisms of electron storage can be influenced.

Visualizing electron storage capacity distribution in biochar through silver tagging.

Electron storage capacity (ESC) is the capacity of a black carbon to store and reversibly donate and accept electrons in redox processes. Electrochemical and chemical analyses have shown the ESC of black carbon (e.g., plant-based biochars) was on the order of a few mmol/g. However, it remains unknown where ESC is located. The spatial distribution of ESC is important because it controls the bioaccessibility of ESC and the rates of biochar redox reactions. Here we used silver to tag the ESC of a wood-derived biochar. Ag+ was allowed to diffuse into the pores of reduced biochar at a constant pH. Up to 2.49 mmol Ag+/g biochar (corresponding to 62% of its ESC) was reduced to Ago nanoparticles (nAg), which served as an ESC marker and was visualized by electron microscopy. Abundant and dense nAg were observed on the biochar surface. In addition, microtomed samples showed ubiquitous and well-dispersed nAg in the interior of biochar, which explains pore diffusion-limited redox reactions and the partial bioaccessibility of its ESC. In addition to probing ESC distribution in black carbon, this method represents a new, ESC-based approach to incorporate large quantities of Ag and other redox-active elements into carbon media for potential environmental applications.

Visualizing the distribution of black carbon's electron storage capacity using silver.

We have developed a method that combines chemical reduction, silver tagging, and electron microscopy (EM) for visualizing the electron storage capacity (ESC) of black carbon (BC). ESC is a BC's capacity to store and reversibly exchange electrons with abiotic and microbial agents, processes that are relevant to biochemistry, greenhouse gas production, contaminant fate, and remediation. In addition to the amount of electrons BC can store, the locations and spatial distribution of ESC on and inside biochar are critical for understanding the bioaccessibility of ESC and the kinetics of redox reactions involving BC. To locate the ESC in a BC particle, we fully reduced a BC, removed excess reductant, and applied silver ion (Ag+) as a tagging agent that diffused into BC to react with functional groups where electrons were stored (i.e., ESC) to form silver nanoparticles (nAg). The nAg deposited on and inside BC were then imaged using multiple EM techniques to visualize the locations and distribution of the ESC. The method is a new and potentially useful tool for investigating ESC production and for elucidating BC-mediated redox transformation.•Novel method to probe and assess the distribution of ESC on/within BC.•Visual confirmation of significant ESC both on the surface and in the interior of BC.•A new method to incorporate silver or other redox-sensitive elements into a carbon medium.

Efficient day-night photocatalysis performance of 2D/2D Ti3C2/Porous g-C3N4 nanolayers composite and its application in the degradation of organic pollutants.

It is hindered by the limited light time that the development of photocatalysis technology, which is a clean and energy-saving advanced oxidation process. In this work, a 2D/2D Ti3C2/porous g-C3N4 nanolayers composited van der Waals (VDW) heterostructure photocatalyst (Ti3C2/PCN) was prepared by a straightforward vacuum filtration method after an ultrasonic stripping process. In this Ti3C2/PCN composite photocatalyst, PCN nanolayers play the role of absorbing visible light, while Ti3C2 nanolayers form VDW heterojunction with PCN nanolayers, which is beneficial to migration of photo-generated electrons from PCN to Ti3C2. The band structure match of Ti3C2/PCN and the build-in electric field from the VDW heterojunction both favor the effective separation and migration of photo-induced charge carriers that is why the Ti3C2/PCN composite shows good day-photocatalytic capability with 98% phenol removal efficiency. Besides, as a good electronic storage material, the Ti3C2 can store excess photo-generated electrons under light irradiation and release them when exposed to electron acceptors in the dark condition. Therefore, the night-photocatalysis can work out even without sunlight, in which 32% phenol was decomposed. In addition, the universality of Ti3C2/PCN day-night photocatalytic system is proved by the degradation of various organic pollutants. The design of this day-night photocatalyst can facilitate the application of photocatalytic reaction to actual environmental scenes, since it reduces the limitation imposed by the presence or absence of sunlight.

New methods for assessing electron storage capacity and redox reversibility of biochar.

Black carbon such as biochar has been shown to support microbial redox transformation by accepting and/or donating electrons. Electron storage capacity (ESC) is an important property that determines the capacity of a biochar to mediate redox processes in natural and engineered systems. However, it remained unclear whether a biochar's ESC is constant and reversible and if so to what extent, over what redox potential range ESC is distributed, and what fraction of the ESC is microbially accessible. In this study, we developed chemical methods that employed combinations of reductants and oxidants of different potentials - Ti(III) citrate, ferricyanide, dithionite, and dissolved O2 - to measure the ESC of Soil Reef biochar, a wood-derived biochar that can serve as an electron donor or acceptor for Geobacter metallireducens. For a given oxidant-reductant pair, the ESC obtained over multiple redox cycles was constant and fully reversible, though lower than that of the virgin biochar. Pore diffusion within biochar particles was rate-limiting and controlled the timescale for redox equilibrium. Results suggest that redox-facile functional groups in biochar were distributed over a broad range of potentials. The ESC measured using dithionite indicates approximately 22% of the biochar's reversible ESC was accessible to G. metallireducens. We propose that reversible ESC may be regarded as a constant and quantifiable property of black carbon.

Transitional Metal Catalytic Pyrite Cathode Enables Ultrastable Four-Electron-Based All-Solid-State Lithium Batteries.

All-solid-state batteries can enable reversible four lithium ion storage for pyrite (FeS2) at a cutoff voltage of 1.0-3.0 V. However, strain/stress concentration generating electrode pulverization and sluggish electrochemical reaction of lithium sulfide and sulfur will affect the long cycling stability of the battery. Through experiments and density functional theory (DFT) calculations, it is proved that nanostructure engineering and electronic conduction improvement with introduction of catalytic cobalt can effectively improve the electrochemical activity of FeS2. The optimized loose structured Co0.1Fe0.9S2 based all-solid-state lithium batteries show reversible capacities of 860.5, 797.7, 685.8, and 561.8 mAh g-1 after five cycles at 100, 200, 500, and 1000 mA g-1, respectively, and a stable capacity of 543.5 mAh g-1 can be maintained after cycling at a current density of 500 mA g-1 for 100 cycles. Ex situ TEM and Raman results reveal that, after the first cycle, the reversible reaction 2Li2S + Fe ↔ FeSy + (2 - y)S + 4Li+ + 4e- proceeds from the following cycles onward, while nanocrystalline mackinawite FeS, Fe(III)-containing mackinawite FeS, and Fe3S4 are generated after the first discharge-charge process. This work provides a facile method for improving the electrochemical performance for multi-electron reaction mechanism based all-solid-state lithium batteries.