Systematically tuning the conductivity of metal−organic frameworks (MOFs) is key to synergizing their attractive synthetic control and porosity with electrochemical attributes useful in energy and sensing technologies. A priori control of charge transfer is possible by exploiting the solid-solution properties of MOFs together with electronic self-exchange enabled by redox pendants. Here we introduce a new strategy for preparing redox-active MOF thin-film electrodes with finely tuned redox pendant content. Varying the ratios of alkylferrocene containing redox-active and inactive links during MOF synthesis enabled the fabrication of electrodes with tunable redox conductivity. The prepared MOF electrodes display maximum electron conductivity of 1.10 mS m −1 , with crystallographic and electrochemical stability upon thousands of redox cycles. Electroanalytical studies demonstrated that the conductivity follows solution-like diffusion-controlled behavior with nonlinear electron diffusion coefficients consistent with charge hopping and percolation models of spatially fixed redox centers. Our studies create new prospects in the design and synthesis of redox-active MOFs with targeted properties for the design of advanced electrochemical devices.

Understanding and controlling chemical dynamics at electrode interfaces is key to electrochemical applications in sensing, electrocatalysis, and energy storage. Here, we introduce colocalized surface-enhanced Raman scattering-scanning electrochemical microscopy (SERS-SECM) as a multimodal tool able to simultaneously probe and affect electrochemical interfaces in real time. As a model system to demonstrate SERS-SECM, we used a self-assembled monolayer of 4-mercaptopyridine (4MPy), a pH sensitive Raman indicator, anchored to silver nanoparticles as a substrate. We modulated the local pH at the surface with chronoamperometry, inducing the hydrogen evolution reaction (HER) at the SECM tip and observed subsequent Raman peak height changes in the 4MPy. We then performed cyclic voltammetry of HER at the SECM tip while measuring SERS spectra every 200 ms to highlight the technique's real-time capabilities. Our results show the capability to sensitively interrogate and trigger chemical/electrochemical dynamic surface phenomena. We hope SERS-SECM will provide insight on the link between heterogeneous and homogeneous reactivity at electrochemical interfaces.

Graphitic carbon electrodes are central to many electrochemical energy storage and conversion technologies. Probing the behavior of molecular species at the electrochemical interfaces they form is paramount to understanding redox reaction mechanisms. Combining surface-enhanced Raman scattering (SERS) with electrochemical methods offers a powerful way to explore such mechanisms, but carbon itself is not a SERS activating substrate. Here, we report on a hybrid substrate consisting of single- or few- layer graphene sheets deposited over immobilized silver nanoparticles which allows for simultaneous SERS and electrochemical interrogation. To demonstrate the viability of our substrate, we adsorbed anthraquinone-2,6-disulfonate (AQDS) to the graphene and studied its redox response simultaneously using SERS and cyclic voltammetry in acidic solutions. We identified spectral changes consistent with the reversible redox of the quinone/hydroquinone pair. The SERS intensities on bare silver and hybrid substrates were on the same order of magnitude, while no discernable signals were observed over bare graphene, confirming the SERS effect on adsorbed molecules. This work provides new prospects for exploring and understanding electrochemical processes in situ at graphitic carbon electrodes.

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Lead acid batteries (LABs) remain an inexpensive energy storage technology with a wide application base. However, their short cycle lifetimes necessitate improved recycling and maintenance technologies to combat their various failure modes. One major cause of failure is hard sulfation, where the formation of large PbSO 4 crystals on the negative active material impedes electron transfer. Here, we introduce a protocol to remove hard sulfate deposits on the negative electrode while maintaining their electrochemical viability for subsequent electrodeposition into active Pb. Soaking the hard sulfate negative electrode in an alkaline EDTA solution reshaped the surface by solubilizing PbSO 4 to Pb-EDTA while avoiding underlying Pb phases. Thereafter, we explored electrodeposition of the Pb-EDTA complex as fresh electrode material and found reduction of Pb-EDTA required lower deposition overpotentials with decreasing pH. We used electrodeposited films on gold to demonstrate cycling of the restored active Pb in H 2 SO 4 . The film's capacity gradually faded with cycling and PbSO 4 formation, alike to commercial LABs. Lastly, we demonstrated the electrodeposition of Pb directly onto negative electrodes from a commercial LAB. Our unique approach seeds opportunity for recycling the electrode materials inside LABs without disassembly or extensive material processing.