Search

Urea electrolysis can address pressing environmental concerns caused by urea-containing wastewater while realizing energy-saving hydrogen production. Highly efficient and affordable electrocatalysts are indispensable for realizing the great potential of this emerging technology. Among the numerous candidates, α-Ni(OH)2has the merits of good electrocatalytic activity, adjustable heteroelement doping, and low cost; consequently, it has received tremendous attention in the electrolytic fields. Herein, a Y3+-doping strategy is developed to effectively enhance the catalytic performance of nickel hydroxide in the urea oxidation reaction (UOR). Our results show that Y3+incorporation successfully modulates the electronic structure of α-Ni(OH)2by inducing Ni3+formation in the crystal lattice to initiate direct UOR, facilitates the Ni3+/Ni2+redox transition with higher current responses to promote indirect UOR, and maintains the structural stability of YNi-10 (Ni2+/Y3+molar ratio = 1:0.1) during long-term UOR operation. Owing to these features, the obtained YNi-10 sample exhibits a higher current density (127 vs 79 mA cm–2at 1.5 V), a lower Tafel slope (48 vs 75 mV dec–1), a larger potential difference between the UOR and oxygen evolution reaction (OER, 0.26 vs 0.22 V at 80 mA cm–2), a higher reaction rate constant (1.1 × 105vs 3.1 × 103cm3mol–1s–1), and a reduced activation energy of UOR (2.9 vs 14.8 kJ mol–1) compared with the Y-free counterpart (YNi-0). This study presents a promising strategy to simultaneously boost direct and indirect UORs, providing new insights for further developing high-performance electrocatalysts.

Polydopamine (PDA) is well known as a mussel-inspired adhesive material composed of oligomeric heteropolymers. However, the conventional eumelanin-like structural assumption of PDA seems deficient in explaining its interfacial adhesion. To determine the decisive mechanism of PDA coating formation, experiments and simulations were performed in this study. 5,6-Dihydroxyindole (DHI), the signature building block of eumelanin, was introduced as the control group. Various typical building blocks in PDA were quantified by physicochemical characterizations, and the polar-group-dominated interfacial interaction was evaluated by classic molecular dynamics and metadynamics methods. Aminoethyl has been proven to be the key functional group inducing the adsorption of PDA on the hydroxylated silica substrates, while DHI shows limited adhesion to the substrate due to the absence of aminoethyl as the catechol-indole structure of DHI exhibits poor affinity to the silica surface. Pyrrole carboxylic acid, as an oxidative product detected from PDA/DHI, is unfavorable for its adhesion to silica substrates. Overall, the coating formation and self-aggregating precipitation of PDA are two competitive aminoethyl-consuming paths; thus, the in situ oxidative coupling of dopamine is indispensable for the PDA coating preparation. The collected PDA precipitates can no longer present satisfactory coating forming behavior, resulting from a shortage of aminoethyl moieties.

Cu–In metallic hybrid is a promising non-noble catalyst for selective electrochemical CO2reduction (eCO2R) to CO, but the lack of direct assembly with a gas diffusion electrode (GDE) limits the further development of eCO2R to CO with both high Faradaic efficiency (FE) and high current density. In this study, an in situ electrochemical spontaneous precipitation (ESP) method was applied for the first time to prepare GDE-combined Cu–In electrocatalysts. The optimum Cu–In catalyst consists of a nanoscale “core–shell” structure of polycrystalline CuxO covered by the amorphous In(OH)3interface. Higher than 90% FE of CO production has been achieved. With the synergy of a GDE flow cell and 1 M KOH catholyte, a current density of ∼200 mA cm–2was reached at −1.17 V (reversible hydrogen electrode), which enabled a CO yield efficiency record of 3.05 mg min–1(CO2/15 mL min–1with a 2 cm2electrode). The ratios between CO and H2produced can be effectively modulated via fine-tuning ESP conditions demonstrating possibility of generating CO or syngas with tuneable ratios. The present study provides a simple approach for constructing novel catalytic interfaces with dual active centers for eCO2R and other emerging electrochemical catalysis research.

Tailoring the binary metal oxide along with developing new synthetic methods for controlling resultant nanostructures in a predictive way is an essential requirement for achieving the further improved electrochemical performance of pseudocapacitors. Here, through a rational design of the supersaturation-mediated driving force for hydrothermal nucleation and crystal growth, we successfully obtain one-dimensional (1-D) nickel molybdenum oxide (NiMoO4) nanostructures with controlled aspect ratios. The morphology of the 1-D NiMoO4nanostructures can be tuned from a low to a high aspect ratio (over a range of diameter sizes from 80 to 800 nm). Such a controllable structure provides a platform for understanding the electrochemical relationships in terms of fast relaxation times and improved ion-diffusion coefficients. We show that the 1-D NiMoO4electrode with a high aspect ratio (HAR) exhibits a much higher specific capacitance of 1335 F g–1at a current density of 1 A g–1compared to the other electrodes with a relatively low aspect ratio, which is due to the unique physical and chemical structure being suitable for electrochemical kinetics. We further demonstrate that an asymmetric supercapacitor consisting of the tailored HAR-NiMoO4electrode can achieve an energy density of 40.7 Wh kg–1and a power density of 16 kW kg–1.

The oxygen evolution reaction (OER) plays a key role in determining the performance of overall water splitting, while a core technological consideration is the development of cost-effective, efficient, and durable catalysts. Here, we demonstrate a robust reduced Fe-oxide@NiCo2O4bilayered non-precious-metal oxide composite as a highly efficient OER catalyst in an alkaline medium. A bilayered oxide composite film with an interconnected nanoflake morphology (Fe2O3@NiCo2O4) is reduced in an aqueous NaBH4solution, which results in a mosslike Fe3O4@NiCo2O4(reduced Fe-oxide@NiCo2O4; rFNCO) nanostructured film with an enhanced electrochemical surface area. The rFNCO film demonstrates an outstanding OER activity with an extraordinary low overpotential of 189 mV at 10 mA cm–2(246 mV at 100 mA cm–2) and a remarkably small Tafel slope of 32 mV dec–1. The film also shows excellent durability for more than 50 h of continuous operation, even at 100 mA cm–2. Furthermore, density functional theory calculations suggest that the unintentionally in situ doped Ni during the reduction reaction possibly improves the OER performance of the rFNCO catalyst shifting d-band centers of both Fe and Ni active sites.