Formation of HO in Near-Neutral Zn-air Batteries Enables Efficient Oxygen Evolution Reaction.

Rechargeable Zn-air batteries (ZABs) with near-neutral electrolytes hold promise as cheap, safe and sustainable devices, but they suffer from slow charge kinetics and remain poorly studied. Here we reveal a charge storage mechanism of near-neutral Zn-air batteries that is mediated by formation of dissolved hydrogen peroxide upon cell discharge and its oxidation upon charge. This HO-mediated pathway facilitates oxygen evolution reaction (OER) at ~1.

Switchable molecular electrocatalysis.

We demonstrate a switchable electrocatalysis mechanism modulated by hydrogen bonding interactions in ligand geometries. By manipulating these geometries, specific electrochemical processes at a single catalytic site can be selectively and precisely activated or deactivated. The α geometry enhances dioxygen electroreduction (ORR) while inhibiting protium redox processes, with the opposite effect seen in the β geometry.

Ligand Isomerization Driven Electrocatalytic Switching.

The prevailing view about molecular catalysts is that the central metal ion is responsible for the reaction mechanism and selectivity, whereas the ligands mainly affect the reaction kinetics. Here, we question this paradigm and show that ligands have a dramatic influence on the selectivity of the product. We show how even a seemingly small change in ligand isomerization sharply alters the selectivity of the well-researched oxygen reduction reaction (ORR) Co phthalocyanine catalyst from an indirect 2e to a direct 4e pathway.

Local CO reservoir layer promotes rapid and selective electrochemical CO reduction.

Electrochemical CO reduction reaction in aqueous electrolytes is a promising route to produce added-value chemicals and decrease carbon emissions. However, even in Gas-Diffusion Electrode devices, low aqueous CO solubility limits catalysis rate and selectivity. Here, we demonstrate that when assembled over a heterogeneous electrocatalyst, a film of nitrile-modified Metal-Organic Framework (MOF) acts as a remarkable CO-solvation layer that increases its local concentration by ~27-fold compared to bulk electrolyte, reaching 0.

Electrochemical energy storage in an organic supercapacitor a non-electrochemical proton charge assembly.

Contrary to conventional beliefs, we show how a functional ligand that does not exhibit any redox activity elevates the charge storage capability of an electric double layer a proton charge assembly. Compared to an unsubstituted ligand, a non-redox active carboxy ligand demonstrated nearly a 4-fold increase in charge storage, impressive capacitive retention even at a rate of 900C, and approximately a 2-fold decrease in leakage currents with an enhancement in energy density up to approximately 70% a non-electrochemical route of proton charge assembly. Generalizability of these findings is presented with various non-redox active functional units that can undergo proton charge assembly in the ligand.

Unprecedented energy storage in metal-organic complexes constitutional isomerism.

The essence of any electrochemical system is engraved in its electrical double layer (EDL), and we report its unprecedented reorganization by the structural isomerism of molecules, with a direct consequence on their energy storage capability. Electrochemical and spectroscopic analyses in combination with computational and modelling studies demonstrate that an attractive field-effect due to the molecule's structural-isomerism, in contrast to a repulsive field-effect, spatially screens the ion-ion coulombic repulsions in the EDL and reconfigures the local density of anions. In a laboratory-level prototype supercapacitor, those with β-structural isomerism exhibit nearly 6-times elevated energy storage compared to the state-of-the-art electrodes, by delivering ∼535 F g at 1 A g while maintaining high performance metrics even at a rate as high as 50 A g.

Unusual Ligand Assistance in Molecular Electrocatalysis via Interfacial Proton Charge Assembly.

We show that the ability of the ligand to reorganize the electric double layer (EDL) often dominates the electrocatalysis contrary to their inductive effect in the spectrochemical series, leading to counterintuitive electrocatalysis. With water oxidation and chlorine evolution as the probe reactions, the same catalytic entity with carboxy functionalized ligand exhibited surprisingly higher electrochemical activity in comparison to the aggressively electron-withdrawing nitro functionalized ligands, which is contrary to their actual location in the spectrochemical series. Spectroscopic and electrochemical analyses suggest the enrichment of catalytically active species in the carboxy substituted ligand via proton charge assembly in the EDL that in turn enhances the kinetics of the overall electrochemical process.

Coulombic Force Gated Molecular Transport in Redox Flow Batteries.

The interfacial electrochemistry of reversible redox molecules is central to state-of-the-art flow batteries, outer-sphere redox species-based fuel cells, and electrochemical biosensors. At electrochemical interfaces, because mass transport and interfacial electron transport are consecutive processes, the reaction velocity in reversible species is predominantly mass-transport-controlled because of their fast electron-transfer events. Spatial structuring of the solution near the electrode surface forces diffusion to dominate the transport phenomena even under convective fluid-flow, which in turn poses unique challenges to utilizing the maximum potential of reversible species by either electrode or fluid characteristics.

Geometrical Isomerism Directed Electrochemical Sensing.

We report the independent role of isomerism of secondary sphere substituents over their nature, a factor often overlooked in molecular electrocatalysis pertaining to electrochemical sensing, by establishing that isomerism redefines the electronic structure at the catalytic reaction center via geometrical factors. UV-vis spectroscopy and X-ray photoelectron spectroscopy suggest that a substituent's isomerism in molecular catalysts conjoins molecular planarity and catalytic activation through competing field effects and resonance effects. As a classical example, we demonstrate the influence of isomerism of the -NO substituents for the electrocatalytic multi electron oxidation of As(III), a potentially important electrochemical pathway for water remediation and arsenic detection.

Unprecedented Isomerism-Activity Relation in Molecular Electrocatalysis.

The role of electrocatalysts in energy storage/conversion, biomedical and environmental sectors, green chemistry, and much more has generated enormous interest in comprehending their structure-activity relations. While targeting the surface-to-volume ratio, exposing reactive crystal planes and interfacial modifications are time-tested considerations for activating metallic catalysts; it is primarily by substitution in molecular electrocatalysts. This account draws the distinction between a substituent's chemical identity and isomerism, when regioisomerism of the -NO substituent is conferred at the "α" and "β" positions on the macrocycle of cobalt phthalocyanines.

A zinc-quinone battery for paired hydrogen peroxide electrosynthesis.

Hydrogen peroxide is a commodity chemical with immense applications as an environmentally benign disinfectant for water remediation, a green oxidant for synthetic chemistry and pulp bleaching, an energy carrier molecule and a rocket propellant. It is typically synthesized by indirect batch anthraquinone process, where sequential hydrogenation and oxidation of anthraquinone molecules generates HO. This highly energy demanding catalytic sequence necessitates the advent of new reaction pathways with lower energy expenditure.

Metal Coordination Polymer Framework Governed by Heat of Hydration for Noninvasive Differentiation of Alkali Metal Series.

We illustrate that the extent of hydration and consequently the heat of hydration of alkali metal ions can be utilized to control their insertion/deinsertion chemistry in a redox active metal coordination polymer framework (CPF) electrode. The formal redox potential of CPF electrode for cation intercalation is inversely correlated to hydrated ionic radii, with clear distinction between the intercalation of ions across alkali metal series. This leads to noninvasive identification and differentiation of cations in the alkali metal series by utilizing a single sensing platform.

A hybrid hydrazine redox flow battery with a reversible electron acceptor.

Hydrazine is a pollutant with high hydrogen content, offering tremendous possibilities in a direct hydrazine fuel cell (DHFC) as it can be converted into electricity via benign end products. Due to the inner sphere nature of half-cell chemistries, hydrazine cross over triggers parasitic chemistry at the Pt-based air cathode of a state-of-the-art DHFC, overly complicating the already sluggish electrode kinetics at the positive electrode. Here, we illustrate that by altering the interfacial chemistry of the catholyte from inner sphere to outer sphere, the parasitic chemistry can be dissociated from the redox chemistry of the electron acceptor and the hybrid fuel cell can be driven by simple carbon-based cathodes.

A Rechargeable Hydrogen Battery.

We utilize proton-coupled electron transfer in hydrogen storage molecules to unlock a rechargeable battery chemistry based on the cleanest chemical energy carrier molecule, hydrogen. Electrochemical, spectroscopic, and spectroelectrochemical analyses evidence the participation of protons during charge-discharge chemistry and extended cycling. In an era of anthropogenic global climate change and paramount pollution, a battery concept based on a virtually nonpolluting energy carrier molecule demonstrates distinct progress in the sustainable energy landscape.

An Electrochemical Wind Velocity Sensor.

Electrochemical interfaces invariably generate unipolar electromotive force because of the unidirectional nature of electrochemical double layers. Herein we show an unprecedented generation of a time varying bipolar electric field between identical half-cell electrodes induced by tailored interfacial migration of magnetic particles. The periodic oscillation of a bipolar electric field is monotonically correlated with velocity-dependent torque, opening new electrochemical pathways targeting velocity monitoring systems.

Fuel Exhaling Fuel Cell.

State-of-the-art proton exchange membrane fuel cells (PEMFCs) anodically inhale H fuel and cathodically expel water molecules. We show an unprecedented fuel cell concept exhibiting cathodic fuel exhalation capability of anodically inhaled fuel, driven by the neutralization energy on decoupling the direct acid-base chemistry. The fuel exhaling fuel cell delivered a peak power density of 70 mW/cm at a peak current density of 160 mA/cm with a cathodic H output of ∼80 mL in 1 h.

A Direct Alcohol Fuel Cell Driven by an Outer Sphere Positive Electrode.

Molecular oxygen, the conventional electron acceptor in fuel cells poses challenges specific to direct alcohol fuel cells (DAFCs). Due to the coupling of alcohol dehydrogenation with the scission of oxygen on the positive electrode during the alcohol crossover, the benchmark Pt-based air cathode experiences severe competition and depolarization losses. The necessity of heavy precious metal loading with domains for alcohol tolerance in the state of the art DAFC cathode is a direct consequence of this.

Redox Active Binary Logic Gate Circuit for Homeland Security.

Bipolar junction transistors are at the frontiers of modern electronics owing to their discrete voltage regulated operational levels. Here we report a redox active binary logic gate (RLG) which can store a "0" and "1" with distinct operational levels, albeit without an external voltage stimuli. In the RLG, a shorted configuration of half-cell electrodes provided the logic low level and decoupled configuration relaxed the system to the logic high level due to self-charge injection into the redox active polymeric system.

Stereochemistry-Dependent Proton Conduction in Proton Exchange Membrane Fuel Cells.

Graphene oxide (GO) is impermeable to H2 and O2 fuels while permitting H(+) shuttling, making it a potential candidate for proton exchange membrane fuel cells (PEMFC), albeit with a large anisotropy in their proton transport having a dominant in plane (σIP) contribution over the through plane (σTP). If GO-based membranes are ever to succeed in PEMFC, it inevitably should have a dominant through-plane proton shuttling capability (σTP), as it is the direction in which proton gets transported in a real fuel-cell configuration. Here we show that anisotropy in proton conduction in GO-based fuel cell membranes can be brought down by selectively tuning the geometric arrangement of functional groups around the dopant molecules.