Yongqiang Qin

In situ Growth of NixCu1-x Alloy Nanocatalysts on Redox-reversible Rutile (Nb,Ti)O4 Towards High-Temperature Carbon Dioxide Electrolysis

In this paper, we report the in situ growth of NixCu1-x (x = 0, 0.25, 0.50, 0.75 and 1.0) alloy catalysts to anchor and decorate a redox-reversible Nb1.33Ti0.67O4 ceramic substrate with the aim of tailoring the electrocatalytic activity of the composite materials through direct exsolution of metal particles from the crystal lattice of a ceramic oxide in a reducing atmosphere at high temperatures. Combined analysis using XRD, SEM, EDS, TGA, TEM and XPS confirmed the completely reversible exsolution/dissolution of the NixCu1-x alloy particles during the redox cycling treatments. TEM results revealed that the alloy particles were exsolved to anchor onto the surface of highly electronically conducting Nb1.33Ti0.67O4 in the form of heterojunctions. The electrical properties of the nanosized NixCu1-x/Nb1.33Ti0.67O4 were systematically investigated and correlated to the electrochemical performance of the composite electrodes. A strong dependence of the improved electrode activity on the alloy compositions was observed in reducing atmospheres at high temperatures. Direct electrolysis of CO2 at the NixCu1-x/Nb1.33Ti0.67O4 composite cathodes was investigated in solid-oxide electrolysers. The CO2 splitting rates were observed to be positively correlated with the Ni composition; however, the Ni0.75Cu0.25 combined the advantages of metallic nickel and copper and therefore maximised the current efficiencies.

Supercapacitive performance of electrochemically doped TiO2 nanotube arrays decorated with Cu2O nanoparticles

Highly ordered TiO2 nanotube arrays (TNAs) with enhanced electronic conductivity treated by introducing oxygen vacancies have been considered to be a promising electrode material for supercapacitors. In this work, we fabricated electrochemically doped TiO2 nanotube arrays (ED-TNAs) through a facile cyclic voltammetry method, and then deposited the uniformly dispersed Cu2O nanoparticles onto ED-TNAs to synthesise a high performance electrode for a supercapacitor. The ED-TNAs electrode exhibited a high specific capacitance of 5.42 mF cm−2 at a scan rate of 10 mV s−1, which was about 59 times higher than for the pristine TNAs electrode. Moreover, the ED-TNAs were demonstrated to be an appropriate support for Cu2O nanoparticles. The highest specific capacitance of the Cu2O/ED-TNAs electrode could reach 198.7 F g−1 at the current density of 0.2 A g−1, and approximately 88.7% of the initial capacitance was retained after 5000 cycles of galvanostatic charge–discharge.

Integration of mesoporous nickel cobalt oxide nanosheets with ultrathin layer carbon wrapped TiO2 nanotube arrays for high-performance supercapacitors

Decorated TiO2 nanotube array-based electrodes for supercapacitors are successfully fabricated by a facile and green process in this paper. Firstly, TiO2 nanotube arrays are modified with ultrathin carbon layers by in situ pyrolysis with residual ethylene glycol from anodization as a carbon resource, then electroactive materials, nickel cobalt oxides with different stoichiometric nickel and cobalt contents, are synthesized by chemical bath deposition and a controlled post-calcination process. The sample demonstrates a superb specific capacitance of 934.9 F g−1 at a current density of 2 A g−1 and a better rate capability of 865.8 F g−1 at 20 A g−1 while maintaining 92.6% capacity after 5000 cycles at a high current density of 10 A g−1. The outstanding supercapacitive performance is attributed to the unique hierarchical mesoporous architectures and the desirable design of the nanocomposites, and it also suggests that carbon modified TiO2 nanotube arrays decorated with nickel cobalt oxides are promising candidates for supercapacitor applications.

Hierarchical three-dimensional MnO2/carbon@TiO2 nanotube arrays for high-performance supercapacitors

Highly ordered TiO2 nanotube arrays (TNAs) modified by other materials with enhanced conductivity and capacitance have been considered to be promising anode materials for supercapacitors. In this work, carbon@TiO2 nanotube arrays (CTNAs) were firstly synthesized through a calcination process under an Ar atmosphere. Then the hierarchical three-dimensional MnO2/carbon@TiO2 nanotube arrays (CMTNAs) were further developed via hydrothermal deposition of uniformly dispersed MnO2 nanoparticles with the help of the in situ reduction effect of the as-obtained carbon layers. The CTNA electrode exhibited a high area capacitance of 5.58 mF cm−2 at a scan rate of 100 mV s−1, which is about 11 times higher than that of the TiO2 nanotube arrays annealed under an air atmosphere (ATNAs). The highest gravimetric capacitance 521.4 A g−1 was achieved with the CMTNAs at a current density of 2 A g−1, and 88.6% of the initial capacitance could be maintained at a current density of 5 A g−1 up to 2000 cycles via a galvanostatic charge–discharge test.

TiO2 nanotube arrays: a study on the surface electrochemical reactions during the photoelectrochemical process

The surface electrochemical reactions of TiO2 nanotube arrays (NTAs) corresponding to different active species of TiO2 NTAs (·OH, h+, and ·O2−) play key roles during the photoelectrochemical process. Effect of the active species and surface electrochemical reactions are studied by adding capture agents of isopropyl alcohol (IPA) for ·OH, ammonium oxalate ((NH4)2C2O2) for h+, and benzoquinone (BQ) for ·O2− radicals. The changes of photocurrent with addition of capture agents confirm the existence of ·OH, h+, and ·O2− during photoelectrochemical process. IPA and (NH4)2C2O2 additions are found to enhance the photocurrent by accelerating the consumption velocity of h+ indirectly and directly and restricting the chargers recombination. BQ can decrease the photocurrent stepwise to 0 due to the indirect consumption of e− on surface of TiO2 NTAs. The consumption of h+ by forming ·OH is 38% that of the whole consumption of h+. The ratio of chargers recombination is higher than 80.8% that of the whole photogenerated chargers.

A facile route to accelerate the formation of TiO2 nanotube arrays

Highly ordered TiO2 nanotube arrays fabricated by electrochemical anodization of titanium have attracted significant attention due to their splendid promising applications. One of the factors limiting the application of TiO2 nanotube arrays was their long sustaining reaction time by anodic oxidation, usually lasting 6 – 12 h and even longer when systhesizing thicker nanotubular layers. In this paper, we reported for the first time a facile and effective route to accelerate the formation of TiO2 nanotube arrays by proper proportional addition of sodium carbonate(Na2CO3) into the anodization electrolyte. In our experiments, we adopted the 0.3 wt% NH4F + EG (ethylene glycol) + 3.0 vol% H2O electrolyte and we added Na2CO3 with the proportion n(NH4F) : n(Na2CO3) = 1:1, 2:1, 3:1, 4:1 and 5:1. The field-emission scanning electron microscope (FESEM) characterization results suggested the Na2CO3 additives accelerated the growth rate of the TiO2 nanotubes with the quickest growth rate 1100 nm/min when n(NH4F) : n(Na2CO3) = 2:1. Finally, we investigated the mechanism of the Na2CO3 additives accelerating the growth rate of the TiO2 nanotubes. It was believed that the hydrolyzation of the Na2CO3 additives in the electrolytes accelerated the formation of the TiO2 nanotubes and at the same time restrained the chemical dissolution of the formed TiO2 nanotubes.

3D Coral-Like Ni3S2 on Ni Foam as a Bifunctional Electrocatalyst for Overall Water Splitting

High-performance noble metal-free electrocatalysts are extremely desired for overall water splitting, but there are huge challenges. Herein, we report a novel one-step electrochemical anodic oxidation and cathodic deposition strategy to in situ fabricate three-dimensional coral-like Ni3S2 on Ni foam (NF) for electrocatalytic overall water splitting. In a typical two-electrode cell, NF acts as both cathodic and anodic electrodes with thiourea aqueous solution as the electrolyte. The nickel ions from the anodic oxidation of NF are directly used as nickel sources to form 3D coral-like Ni3S2/NF by the cathodic deposition method simultaneously. The optimal 3D Ni3S2/NF-4 electrode shows high electrocatalytic activity for hydrogen evolution reaction and oxygen evolution reaction with low overpotentials of 89 and 242 mV, respectively, to afford 10 mA cm-2. When the as-obtained Ni3S2/NF-4 is used as a bifunctional electrocatalyst in an electrolyzer, a low applied voltage of 1.577 V is needed to reach 10 mA cm-2, with extremely long durability. This work focuses on the rational design of unique structures as efficient non-noble metal-based electrocatalysts, which hold great potential for practical applications in electrocatalytic water splitting.