In light of the enormous energy footprint of the Haber-Bosch process (1-2% of global energy consumption), alternative green routes of generating ammonia (NH3) are needed. The electrochemical reduction of NO3-...

In this manuscript, we design non-precious-metal electrocatalysts for the O2 reduction reaction (ORR) based on Cu complexes of the tripeptide glutathione modified with ferrocene (Cu-GSH-NHFc). Homogenous catalysis experiments demonstrate that the covalently bound Cu-GSH-NHFc catalyst exhibits enhanced activity compared to mixtures of the individual catalyst components. Heterogeneous catalysis results on rotating disk electrodes (RDE) and rotating ring-disk electrodes (RRDE) show that Cu-GSH-NHFc catalyzes the ORR via a four-electron pathway at pH 4–7, while the same catalyst without ferrocene produces significant quantities of H2O2. Cyclic voltammetry reveals electronic coupling between the appended ferrocene moieties and the Cu active site. From these studies, we propose an ORR reaction pathway, in which fast electron transfer facilitated by ferrocene explains the high selectivity of the Cu-GSH-NHFc catalyst. We envision that this understanding will lead to future developments in the design of non-precious-metal ORR catalysts, which are instrumental to fuel cell technologies.

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Electrocatalytic NH 3 production from NO 3 − reduction is a promising alternative to traditional Haber-Bosch NH 3 synthesis. Although Nafion is commonly employed as a separator in two-compartment electrochemical cells and as a binder in catalyst inks, in this manuscript, we use Nafion as an overlayer on top of Cu electrodeposits to enhance NH 3 selectivity. Faradaic efficiencies for NH 3 and NO 2 − generation were evaluated as a function of electrodeposit morphology with and without the Nafion layer. These studies reveal that the combination of Cu (220) faces in the electrodeposits and activation of a NO intermediate by Nafion enables NH 3 production with a high Faradaic efficiency of (97.0 ± 0.3) %. This optimized architecture also exhibits the fastest rate of NH 3 production among the catalysts studied even after normalizing for its rough electrochemical active surface area. In addition to voltammetry, the electrocatalysts were characterized using a variety of techniques including atomic force microscopy, scanning electron microscopy, X-ray diffraction, and water contact angle measurements. Insights garnered about the parameters needed for selective NH 3 production will inform future research on nonprecious metal NO 3 − reduction catalysts.

The sluggishness of the O 2 reduction reaction (ORR) is the most significant challenge to fuel cell commercialization. Cu-based ORR catalysts are promising non-precious metal alternatives to Pt. In this study, we synthesize four different Cu 2+ complexes of tripeptides (Cu−GSHAmide, Cu−NCG, Cu−ECG, and Cu−QCG) and analyze the relationships between their electrocatalytic activities and physicochemical properties. Rotating ring-disk electrode experiments indicate that the catalytic current densities and selectivities vary widely as a function of pH and peptide identity. Through Fourier transform infrared spectroscopy, we describe the nature of the intermolecular forces between the peptides studied along with those of the corresponding Cu 2+ complexes. This analysis allows us to quantify the degree of peptide aggregation in the ORR electrocatalysts. Combined with the Cu 2+ −peptide binding constants, we develop models that accurately predict how peptide aggregation dictates catalyst current density and selectivity for the four-electron reduction of O 2 to water. These models indicate that Cu 2+ −peptide ORR electrocatalysts with relatively strong binding constants and weak peptide aggregation exhibit increased selectivity and enhanced kinetics. This central finding highlights an important set of design rules for the development of future highperformance Cu ORR electrocatalysts.