Cobalt–Iron (Oxy)hydroxide Oxygen Evolution Electrocatalysts: The Role of Structure and Composition on Activity, Stability, and Mechanism

Cobalt oxides and (oxy)­hydroxides have been widely studied as electrocatalysts for the oxygen evolution reaction (OER). For related Ni-based materials, the addition of Fe dramatically enhances OER activity. The role of Fe in Co-based materials is not well-documented. We show that the intrinsic OER activity of Co_1–<i>x</i>Fe_<i>x</i>(OOH) is ∼100-fold higher for <i>x</i> ≈ 0.6–0.7 than for <i>x</i> = 0 on a per-metal turnover frequency basis. Fe-free CoOOH absorbs Fe from electrolyte impurities if the electrolyte is not rigorously purified. Fe incorporation and increased activity correlate with an anodic shift in the nominally Co^2+/3+ redox wave, indicating strong electronic interactions between the two elements and likely substitutional doping of Fe for Co. <i>In situ</i> electrical measurements show that Co_1–<i>x</i>Fe_<i>x</i>(OOH) is conductive under OER conditions (∼0.7–4 mS cm^–1 at ∼300 mV overpotential), but that FeOOH is an insulator with measurable conductivity (2.2 × 10^–2 mS cm^–1) only at high overpotentials >400 mV. The apparent OER activity of FeOOH is thus limited by low conductivity. Microbalance measurements show that films with <i>x</i> ≥ 0.54 (i.e., Fe-rich) dissolve in 1 M KOH electrolyte under OER conditions. For <i>x</i> < 0.54, the films appear chemically stable, but the OER activity decreases by 16–62% over 2 h, likely due to conversion into denser, oxide-like phases. We thus hypothesize that Fe is the most-active site in the catalyst, while CoOOH primarily provides a conductive, high-surface area, chemically stabilizing host. These results are important as Fe-containing Co- and Ni-(oxy)­hydroxides are the fastest OER catalysts known

Optimisation of the preservation conditions for molecularly imprinted polymer nanoparticles specific for trypsin

The influence of lyophilisation, autoclaving and sonication on the stability and performance of trypsin-specific molecularly imprinted polymer nanoparticles (MIP NPs) has been studied in order to improve their long-term physical stability. Glucose, glycine, sorbitol and trehalose were tested as cryoprotectant agents during the lyophilisation treatment. The effect of lyophilisation and sterilisation on affinity of trypsin-specific NPs was assessed using Biacore 3000 instrument. The results have demonstrated that MIP NPs successfully withstood the lyophilisation and autoclaving conditions without a reduction of their recognition properties and affinity. It is possible to conclude that both tested lyophilisation and sterilisation treatments were suitable for a long-term storage of the prepared MIP NPs and could be used to store MIP NPs in dry state and hence reduce the chance of the bacterial contamination. An effective preservation of the MIP NPs is a crucial requirement for their future applications in the clinical diagnostics and bioimaging

Amorphous In–Ga–Zn Oxide Semiconducting Thin Films with High Mobility from Electrochemically Generated Aqueous Nanocluster Inks

Solution processing is a scalable means of depositing large-area electronics for applications in displays, sensors, smart windows, and photovoltaics. However, solution routes typically yield films with electronic quality inferior to traditional vacuum deposition, as the solution precursors contain excess organic ligands, counterions, and/or solvent that leads to porosity in the final film. We show that electrolysis of aq. mixed metal nitrate salt solutions drives the formation of indium gallium zinc oxide (IGZO) precursor solutions, without purification, that consist of ∼1 nm radii metal–hydroxo clusters, minimal nitrate counterions, and no organic ligands. Films deposited from cluster precursors over a wide range of composition are smooth (roughness of 0.24 nm), homogeneous, dense (80% of crystalline phase), and crack-free. The transistor performance of IGZO films deposited from electrochemically synthesized clusters is compared to those from the starting nitrate salt solution, sol–gel precursors, and, as a control, vacuum-sputter-deposited films. The average channel mobility (μ_<i>AVE</i>) of air-annealed cluster films (In:Ga:Zn = 69:12:19) at 400 °C was ∼9 cm² V^–1 s^–1, whereas those of control nitrate salt and sol–gel precursor films were ∼5 and ∼2 cm² V^–1 s^–1, respectively. By incorporating an ultrathin indium–tin–zinc oxide interface layer prior to IGZO film deposition and air-annealing at 550 °C, a μ_<i>AVE</i> of ∼30 cm² V^–1 s^–1 was achieved, exceeding that of sputtered IGZO control films. These data show that electrochemically derived cluster precursors yield films that are structurally and electrically superior to those deposited from metal nitrate salt and related organic sol–gel precursor solutions and approach the quality of sputtered films