AgII -Mediated Electrocatalytic Ambient CH4 Functionalization Inspired by HSAB Theory.

Although most class (b) transition metals have been studied in regard to CH4 activation, divalent silver (AgII ), possibly owing to its reactive nature, is the only class (b) high-valent transition metal center that is not yet reported to exhibit reactivities towards CH4 activation. We now report that electrochemically generated AgII metalloradical readily functionalizes CH4 into methyl bisulfate (CH3 OSO3 H) at ambient conditions in 98 % H2 SO4 . Mechanistic investigation experimentally unveils a low activation energy of 13.1 kcal mol-1 , a high pseudo-first-order rate constant of CH4 activation up to 2.8×103  h-1 at room temperature and a CH4 pressure of 85 psi, and two competing reaction pathways preferable towards CH4 activation over solvent oxidation. Reaction kinetic data suggest a Faradaic efficiency exceeding 99 % beyond 180 psi CH4 at room temperature for potential chemical production from widely distributed natural gas resources with minimal infrastructure reliance.

Autonomous closed-loop mechanistic investigation of molecular electrochemistry via automation.

Electrochemical research often requires stringent combinations of experimental parameters that are demanding to manually locate. Recent advances in automated instrumentation and machine-learning algorithms unlock the possibility for accelerated studies of electrochemical fundamentals via high-throughput, online decision-making. Here we report an autonomous electrochemical platform that implements an adaptive, closed-loop workflow for mechanistic investigation of molecular electrochemistry. As a proof-of-concept, this platform autonomously identifies and investigates an EC mechanism, an interfacial electron transfer (E step) followed by a solution reaction (C step), for cobalt tetraphenylporphyrin exposed to a library of organohalide electrophiles. The generally applicable workflow accurately discerns the EC mechanism's presence amid negative controls and outliers, adaptively designs desired experimental conditions, and quantitatively extracts kinetic information of the C step spanning over 7 orders of magnitude, from which mechanistic insights into oxidative addition pathways are gained. This work opens opportunities for autonomous mechanistic discoveries in self-driving electrochemistry laboratories without manual intervention.

Bisulfate as a redox-active ligand in vanadium-based electrocatalysis for CH4 functionalization.

The roles of unforgiving H2SO4 solvent in CH4 activation with molecular catalysts have not been experimentally well-illustrated despite computational predictions. Here, we provide experimental evidence that metal-bound bisulfate ligand introduced by H2SO4 solvent is redox-active in vanadium-based electrocatalytic CH4 activation discovered recently. Replacing one of the two terminal bisulfate ligands with redox-inert dihydrogen phosphate in the pre-catalyst vanadium (V)-oxo dimer completely quenches its activity towards CH4, which may inspire environmentally benign catalysis with minimal use of H2SO4.

Expanding nanoparticle multifunctionality: size-selected cargo release and multiple logic operations.

Physically stimulated nanoparticles that deliver size-selected cargo and function as logic gates are reported. To achieve this goal the particle requires multiple components, and we recognized early on that the components, not just the released cargo, could be used to demonstrate logic operations (OR and AND logic). For stimuli, we chose two non-invasive types, red light and alternating magnetic fields (AMF), because they both have potential biological relevance. To realize cargo delivery with size selection and logic operations, we mechanized the surface of core@shell nanoparticles with a superparamagnetic core that generates localized heating when exposed to an AMF, and a mesoporous silica shell into which cargo molecules with different sizes were loaded. We demonstrate the core@shell nanoparticles can load the dual cargos with different sizes and subsequently release the smaller (∼0.5 nm) and bigger (∼2 nm) cargos in succession when stimulated by a red light followed by an AMF. Finally, we demonstrate that the multi-component nanoparticles could function as nanoparticle-based Boolean logic gates where AMF and red light served as the two inputs and the release of small cargo, and free cyclodextrin served as the outputs. The construction of two Boolean logic gates (OR, and AND) was realized.

Ambient methane functionalization initiated by electrochemical oxidation of a vanadium (V)-oxo dimer.

The abundant yet widely distributed methane resources require efficient conversion of methane into liquid chemicals, whereas an ambient selective process with minimal infrastructure support remains to be demonstrated. Here we report selective electrochemical oxidation of CH4 to methyl bisulfate (CH3OSO3H) at ambient pressure and room temperature with a molecular catalyst of vanadium (V)-oxo dimer. This water-tolerant, earth-abundant catalyst possesses a low activation energy (10.8 kcal mol‒1) and a high turnover frequency (483 and 1336 hr-1 at 1-bar and 3-bar pure CH4, respectively). The catalytic system electrochemically converts natural gas mixture into liquid products under ambient conditions over 240 h with a Faradaic efficiency of 90% and turnover numbers exceeding 100,000. This tentatively proposed mechanism is applicable to other d0 early transition metal species and represents a new scalable approach that helps mitigate the flaring or direct emission of natural gas at remote locations.