Electrocatalytic recycling of waste nitrate (NO3−) to valuable ammonia (NH3) at ambient conditions is a green and appealing alternative to the Haber−Bosch process. However, the reaction requires multi-step electron and proton transfer, making it a grand challenge to drive high-rate NH3 synthesis in an energy-efficient way. Herein, we present a design concept of tandem catalysts, which involves coupling intermediate phases of different transition metals, existing at low applied overpotentials, as cooperative active sites that enable cascade NO3−-to-NH3 conversion, in turn avoiding the generally encountered scaling relations. We implement the concept by electrochemical transformation of Cu−Co binary sulfides into potential-dependent core−shell Cu/CuOx and Co/CoO phases. Electrochemical evaluation, kinetic studies, and in−situ Raman spectra reveal that the inner Cu/CuOx phases preferentially catalyze NO3− reduction to NO2−, which is rapidly reduced to NH3 at the nearby Co/CoO shell. This unique tandem catalyst system leads to a NO3−-to-NH3 Faradaic efficiency of 93.3 ± 2.1% in a wide range of NO3− concentrations at pH 13, a high NH3 yield rate of 1.17 mmol cm−2 h−1 in 0.1 M NO3− at −0.175 V vs. RHE, and a half-cell energy efficiency of ~36%, surpassing most previous reports.

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Photosystem I (PSI), a robust and abundant biomolecule capable of delivering high‐energy photoelectrons, has a great potential for the fabrication of light‐driven semi‐artificial bioelectrodes. Although possibilities have been explored in this regard, the true capabilities of this technology have not been achieved yet, particularly for their use as bioanodes. Here, the use of PSI Langmuir monolayers and their electrical wiring with specifically designed redox polymers is shown, ensuring an efficient mediated electron transfer as the basis for the fabrication of an advanced biophotoanode. The bioelectrode is rationally implemented and optimized for enabling the generation of substantial photocurrents of up to 17.6 µA cm−2 and is even capable of delivering photocurrents at potentials as low as −300 mV vs standard hydrogen electrode, surpassing the performance of comparable devices. To highlight the applicability of the developed light‐driven bioanode, a biophotovoltaic cell is assembled in combination with a gas‐breathing biocathode. The assembly operates in a single compartment cell and delivers considerable power outputs at large cell voltages. The implemented biophotoanode constitutes an important step toward the development of advanced biophotovoltaic devices.

The development of electrodes for efficient CO2 reduction while forming valuable compounds is critical. The use of enzymes as catalysts provides the advantage of high catalytic activity in combination with highly selective transformations. We describe the electrical wiring of a carbon monoxide dehydrogenase II from Carboxydothermus hydrogenoformans (ChCODH II) using a cobaltocene-based low-potential redox polymer for the selective reduction of CO2 to CO over gas diffusion electrodes. High catalytic current densities of up to −5.5 mA cm–2 are achieved, exceeding the performance of previously reported bioelectrodes for CO2 reduction based on either carbon monoxide dehydrogenases or formate dehydrogenases. The proposed bioelectrode reveals considerable stability with a half-life of more than 20 h of continuous operation. Product quantification using gas chromatography confirmed the selective transformation of CO2 into CO without any parasitic co-reactions at the applied potentials.

The lifetime of implantable electrochemical glucose monitoring devices is limited due to the foreign body response and detrimental effects from ascorbic acid (AA) and uric acid (UA) interferents that are components of physiological media. Polymer coatings can be used to shield biosensors from these interferences and prolong their functional lifetime. This work explored several approaches to protect redox polymer-based glucose biosensors against such interferences by designing six targeted multi-layer sensor architectures. Biological interferents, like cells and proteins, and UA and AA interferents were found to have individual effects on the current density and operational stability of glucose biosensors, requiring individual protection and treatment. Protection against biofouling can be achieved using a poly(2-methacryloyloxyethyl phosphorylcholine-co-glycidyl methacrylate) (MPC) zwitterionic polymer coating. An enzyme-scavenging approach was compared to electrostatic repulsion by negatively charged polymers for protection against AA and UA interferences. A multi-layer novel polymer design (PD) system consisting of a crosslinkable negatively charged polyvinylimidazole-polysulfostyrene co-polymer inner layer and a cross-linkable MPC zwitterionic polymer outer layer showed the best protection against AA, UA, and biological interferences. The sensor protected using the novel PD shield displayed the lowest mean absolute relative difference between the glucose reading without the interferent and the reading value with the interferent present and also displayed the lowest variability in sensor readings in complex media. For sensor measurements in artificial plasma, the novel PD extends the linear range (R 2 = 0.99) of the sensor from 0−10 mM for the control to 0−20 mM, shows a smaller decrease in sensitivity, and retains high current densities. The application of PD multi-target coating improves sensor performance in complex media and shows promise for use in sensors operating in real conditions.