Unprecedented energy storage in metal-organic complexes via 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 ß-structural isomerism exhibit nearly 6-times elevated energy storage compared to the state-of-the-art electrodes, by delivering ∼535 F g-1 at 1 A g-1 while maintaining high performance metrics even at a rate as high as 50 A g-1. The elucidation of the decisive role of structural isomerism in reconfiguring the electrified interface represents a major step forward in understanding the electrodics of molecular platforms.

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 -NO2 substituents for the electrocatalytic multi electron oxidation of As(III), a potentially important electrochemical pathway for water remediation and arsenic detection. The isomerism dependent oxidative activation of catalytic center leads to a nonprecious molecular catalyst capable for direct As(III) oxidation with an experimental detection limit close to WHO guidelines. This work opens up an unusual approach in analytical chemistry for developing various sensing platforms for challenging chemical and electrochemical reactions.

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 H2O2. This highly energy demanding catalytic sequence necessitates the advent of new reaction pathways with lower energy expenditure. Here we demonstrate a Zn-quinone battery for paired H2O2 electrosynthesis at the three phase boundary of its cathodic half-cell during electric power generation. The catalytic quinone half-cell of the Zn-quinone battery, mediates proton coupled electron transfer with molecular oxygen during its chemical regeneration thereby pairing peroxide electrosynthesis with electricity generation. Hydrogen peroxide synthesizing Zn-quinone battery (HPSB) demonstrated a peak power density of ~90 mW/cm2 at a peak current density of ~145 mA/cm2 while synthesizing ~230 mM of H2O2. HPSB offers immense opportunities as it distinctly couples electric power generation with peroxide electrosynthesis which in-turn transforms energy conversion in batteries truly multifunctional.

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. Although efforts are dedicated to selectively cleave oxygen, the root of the problem being the inner sphere nature of either half-cell chemistry is often overlooked. Using an outer sphere electron acceptor that does not form a bond with the cathode during redox energy transformation, we effectively decoupled the interfacial chemistry from parasitic chemistry leading to a DAFC driven by alcohol passive carbon nanoparticles, with performance metrics ∼8 times higher than Pt-based DAFC-O2.