Matteo Duca

Glycerol (GlOH) electrooxidation is a potential route to GlOH valorisation. In this work, we show that GlOH oxidation can be enhanced at bimetallic Pt−Ru electrodes with respect to bare Pt in sulphuric acid. We electrodeposited high‐surface area Pt electrodes comprising of 40 % (100) sites, along with a smaller amount of (111) domains. Spontaneous Ru deposition was carried out by immersion in a RuCl₃ solution for a varying amount of time. Voltammetric methods demonstrated that (100) sites are decorated most readily. Pt−Ru electrodes display an earlier onset potential for CO_ads oxidation, which translates into an anticipation of the main GlOH oxidation wave. Under prolonged Ru deposition, Ru decoration also proceeds close to (111) Pt domains, as highlighted by CO stripping. We suggest that such ensembles may play a critical role in achieving optimal GlOH activity at Pt−Ru.

Using de novo protein design, we incorporated a copper metal binding site within the three-helix bundle α₃D (Walsh et al. Proc. Natl. Acad. Sci. U.S.A. 1999, 96, 5486–5491) to assess whether a cupredoxin center within an α-helical domain could mimic the spectroscopic, structural, and redox features of native type-1 copper (CuT1) proteins. We aimed to determine whether a CuT1 center could be realized in a markedly different scaffold rather than the native β-barrel fold and whether the characteristic short Cu–S bond (2.1–2.2 Å) and positive reduction potentials could be decoupled from the spectroscopic properties (ε_600 nm = 5000 M^–1 cm^–1) of such centers. We incorporated 2HisCys(Met) residues in three distinct α₃D designs designated core (CR), chelate (CH), and chelate-core (ChC). XAS analysis revealed a coordination environment similar to reduced CuT1 proteins, producing Cu–S(Cys) bonds ranging from 2.16 to 2.23 Å and Cu–N(His) bond distances of 1.92–1.99 Å. However, Cu(II) binding to the CR and CH constructs resulted in tetragonal type-2 copper-like species, displaying an intense absorption band between 380 and 400 nm (>1500 M^–1 cm^–1) and A_|| values of (150–185) × 10^–4 cm^–4. The ChC construct, which possesses a metal-binding site deeper in its helical bundle, yielded a CuT1-like brown copper species, with two absorption bands at 401 (4429 M^–1 cm^–1) and 499 (2020 M^–1 cm^–1) nm and an A_|| value ∼30 × 10^–4 cm^–4 greater than its native counterparts. Electrochemical studies demonstrated reduction potentials of +360 to +460 mV (vs NHE), which are within the observed range for azurin and plastocyanin. These observations showed that the designed metal binding sites lacked the necessary rigidity to enforce the appropriate structural constraints for a Cu(II) chromophore (EPR and UV–vis); however, the Cu(I) structural environment and the high positive potential of CuT1 centers were recapitulated within the α-helical bundle of α₃D.

Electrocatalytic reduction of nitrate at noble metals is particularly sluggish at neutral pH, while nitrate reductase enzymes are highly active for selective reduction of nitrate to nitrite under these conditions. However, noble metal electrodes can effectively reduce nitrite, even at millimolar concentrations in neutral media. In this study, we demonstrate tandem electrochemical reduction of nitrate to ammonia by combining Escherichia (E.) coli nitrate reductase (NarGHI) on an electrode with Pt or Rh nanoparticles. Under potential control, the enzyme first reduces nitrate to nitrite, which is further reduced by the metal at a slightly more negative potential. This creates a novel electrocatalytic relay cascade where the enzyme overcomes an inherent limitation of the metal. This proof‐of‐concept study, using biological and metal catalysts supported on commercial carbon beads, demonstrates a simple approach to the assembly of ‘hybrid’ electrocatalysts.

From a study of the electrocatalytic reduction of nitrate on Pt and Rh electrodes over a wide pH range, HNO ₃ is suggested as the only reducible species in nitrate reduction on Pt, whereas both HNO ₃ and the nitrate anion are reducible on Rh.