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1. Probing the Effects of Acid Electrolyte Anions on Electrocatalyst Activity and Selectivity for the Oxygen Reduction Reaction

   https://doi.org/10.1002/celc.202100500  

   Zamora Zeledón, José A. ; Kamat, Gaurav Ashish ; Gunasooriya, G. T. Kasun Kalhara ; Nørskov, Jens K. ; Stevens, Michaela Burke ; Jaramillo, Thomas F. ( July 2021 , ChemElectroChem)

   The local microenvironment at the electrode‐electrolyte interface plays an important role in electrocatalytic performance. Herein, we investigate the effect of acid electrolyte anion identity on the oxygen reduction reaction (ORR) activity and selectivity of smooth Ag and Pd catalyst thin films. Cyclic voltammetry in perchloric, nitric, sulfuric, phosphoric, hydrochloric, and hydrobromic acid, at pH 1, reveals that Ag ORR activity trends as follows: HClO₄>HNO₃>H₂SO₄>H₃PO₄>HCl≫HBr, while Pd ORR activity trends as: HClO₄>H₂SO₄>HNO₃>H₃PO₄>HCl≫HBr. Moreover, rotating‐ring‐disk‐electrode selectivity measurements demonstrate enhanced 4e⁻selectivity on both Ag and Pd, by up to 35 %H₂O₂and 10 %H₂O₂respectively, in HNO₃compared to in HClO₄. Relating physics‐based modeling and experimental results, we postulate that ORR performance depends greatly on anion‐related phenomena in the double layer, for instance competitive adsorption and non‐covalent interactions.

    

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2. Simultaneous Analysis of Ascorbic Acid, Uric Acid, and Dopamine at Bare Polystyrene Thermoplastic Electrodes

   https://doi.org/10.1002/celc.202101600  

   McCord, Cynthia P. ; Summers, Bali ; Henry, Charles S. ( March 2022 , ChemElectroChem)

   Simultaneous analysis of ascorbic acid (AA), uric acid (UA), and dopamine (DA) is desirable as they are important biomarkers that coexist in biological fluids. Electrochemical detection of these molecules can be challenging as their oxidation peaks are poorly resolved at most unmodified electrodes. Modifications are typically necessary for analysis which increase cost and complicate fabrication. Herein, inexpensive and moldable polystyrene thermoplastic electrodes (PS TPEs), that can be used for simultaneous analysis of AA, DA, and UA, without surface modification, were presented. Electrode composition was optimized for conductivity, capacitance, and electrochemistry. Detection limits were 4, 0.9, and 4 μmfor AA, DA and UA respectively. PS TPEs were also challenged in urine; excellent recoveries (90–110 %) were seen for AA and UA. DA showed lower recoveries (82 % for 10 μmand 47 % for 5 μm), but in the future, higher recoveries can be achieved through design considerations and further material optimization.

    

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3. Decoupling Electron‐ and Phase‐Transfer Processes to Enhance Electrochemical Nitrate‐to‐Ammonia Conversion by Blending Hydrophobic PTFE Nanoparticles within the Electrocatalyst Layer

   https://doi.org/10.1002/aenm.202203891  

   Gao, Jianan ; Ma, Qingquan ; Young, Joshua ; Crittenden, John C. ; Zhang, Wen ( March 2023 , Advanced Energy Materials)

   Electrochemical upcycling of nitrate into ammonia at ambient conditions offers a sustainable synthesis pathway that can complement the current industrial NH₃production from the Haber–Bosch process. One of the key rate‐limiting steps is the effective desorption of gaseous or interfacial bubble products, mainly NH₃with some minor side products of nitrogen and hydrogen, from the electrode surfaces to sustain available sites for the NO₃⁻reduction reaction. To facilitate the gaseous product desorption from the catalytic sites, hydrophobic polytetrafluoroethylene (PTFE) nanoparticles are blended within a CuO catalyst layer, which is shown to eliminate the undesirable accumulation and blockage of electrode surfaces and largely decouples the electron‐ and phase‐transfer processes. The NH₃partial current density normalized by the electrochemically active surface area (ECSA) increases by nearly a factor of 17.8 from 11.4 ± 0.1 to 203.3 ± 1.8 mA cm⁻²_ECSA. The DFT and ab‐initio molecular dynamics simulations suggest that the hydrophobic PTFE nanoparticles may serve as segregated islands to enhance the spillover and transport the gaseous products from electrocatalysts to the PTFE. Thus, a higher ammonia transfer is achieved for the mixed PTFE/CuO electrocatalyst. This new and simple strategy is expected to act as inspiration for future electrochemical gas‐evolving electrode design.

    

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4. Selective incorporation of 5‐hydroxytryptophan blocks long range electron transfer in oxalate decarboxylase

   https://doi.org/10.1002/pro.4537  

   Pastore, Anthony John ; Montoya, Alvaro ; Kamat, Manasi ; Basso, Kari B. ; Italia, James S. ; Chatterjee, Abhishek ; Drosou, Maria ; Pantazis, Dimitrios A. ; Angerhofer, Alexander ( December 2022 , Protein Science)

   Oxalate decarboxylase fromBacillus subtilisis a binuclear Mn‐dependent acid stress response enzyme that converts the mono‐anion of oxalic acid into formate and carbon dioxide in a redox neutral unimolecular disproportionation reaction. A π‐stacked tryptophan dimer, W96 and W274, at the interface between two monomer subunits facilitates long‐range electron transfer between the two Mn ions and plays an important role in the catalytic mechanism. Substitution of W96 with the unnatural amino acid 5‐hydroxytryptophan leads to a persistent EPR signal which can be traced back to the neutral radical of 5‐hydroxytryptophan with its hydroxyl proton removed. 5‐Hydroxytryptophan acts as a hole sink preventing the formation of Mn(III) at the N‐terminal active site and strongly suppresses enzymatic activity. The lower boundary of the standard reduction potential for the active site Mn(II)/Mn(III) couple can therefore be estimated as 740 mV against the normal hydrogen electrode at pH 4, the pH of maximum catalytic efficiency. Our results support the catalytic importance of long‐range electron transfer in oxalate decarboxylase while at the same time highlighting the utility of unnatural amino acid incorporation and specifically the use of 5‐hydroxytryptophan as an energetic sink for hole hopping to probe electron transfer in redox proteins.

    

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5. Acid–Base Interaction Enhancing Oxygen Tolerance in Electrocatalytic Carbon Dioxide Reduction

   https://doi.org/10.1002/anie.202003093  

   Li, Pengsong ; Lu, Xu ; Wu, Zishan ; Wu, Yueshen ; Malpass‐Evans, Richard ; McKeown, Neil B. ; Sun, Xiaoming ; Wang, Hailiang ( April 2020 , Angewandte Chemie International Edition)

   Hybrid electrodes with improved O₂tolerance and capability of CO₂conversion into liquid products in the presence of O₂are presented. Aniline molecules are introduced into the pore structure of a polymer of intrinsic microporosity to expand its gas separation functionality beyond pure physical sieving. The chemical interaction between the acidic CO₂molecule and the basic amino group of aniline renders enhanced CO₂separation from O₂. Loaded with a cobalt phthalocyanine‐based cathode catalyst, the hybrid electrode achieves a CO Faradaic efficiency of 71 % with 10 % O₂in the CO₂feed gas. The electrode can still produce CO at an O₂/CO₂ratio as high as 9:1. Switching to a Sn‐based catalyst, for the first time O₂‐tolerant CO₂electroreduction to liquid products is realized, generating formate with nearly 100 % selectivity and a current density of 56.7 mA cm⁻²in the presence of 5 % O₂.

    

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