Simultaneous removal of tetracycline hydrochloride and hexavalent chromium by heterogeneous Fenton in a photocatalytic fuel cell system.

In this work, a novel double-chamber system (PFC-Fenton), combined photocatalytic fuel cell (PFC) with Fenton, was constructed for tetracycline hydrochloride (TCH) and hexavalent chromium (Cr(VI)) removal and electricity production. Therein, Zn5(OH)6(CO3)2/Fe2O3/BiVO4/fluorine-doped SnO2 (ZIO/BiVO4/FTO) and carboxylated carbon nanotubes/polypyrrole/graphite felt (CCNTs/Ppy/GF) were served as photoanode and cathode, respectively. Under light irradiation, the removal efficiencies of TCH and Cr(VI) with the addition of H2O2 (2 mL) could reach 93.1% and 80.4%, respectively. Moreover, the first-order kinetic constants (7.37 × 10-3 min-1 of TCH and 3.94 × 10-3 min-1 of Cr(VI)) were 5.26 and 5.57 times as much as the absence of H2O2. Simultaneously, the maximum power density could be obtained 0.022 mW/cm2 at a current density of 0.353 mA/cm2. Therein, the main contribution of TCH degradation was ·OH and holes in anode chamber. The synergistic effect of photoelectrons, generated ·O2-, and H2O2 played a crucial role in the reduction of Cr(VI) in cathode chamber. The high-performance liquid chromatography-mass spectrometry indicated that TCH could be partially mineralized into CO2 and H2O. X-ray photoelectron spectroscope and X-ray absorption near-edge structure spectra showed that Cr(VI) could be reduced to Cr(III). After 5 times of cycling, the removal efficiencies of TCH and Cr(VI) were still greater than 70%, indicating the remarkable stability of the PFC-Fenton system. Overall, this system could remove TCH/Cr(VI) and generate power simultaneously without iron sludge formation, demonstrating a promising method to further develop PFC-Fenton technology.

Interface engineering of hierarchical flower-like N, P, O-doped NixPy self-supported electrodes for highly efficient water-to-hydrogen fuel/oxygen conversion.

Rational construction of efficient bifunctional catalysts with robust catalytic activity and durability is significant for overall water splitting (conversion between water and hydrogen fuel/oxygen) using non-precious metal systems. In this work, the hierarchically porous N, P, O-doped transition metal phosphate in the Ni foam (NF) electrode (hollow flower-like NPO/NixPy@NF) was prepared through facile hydrothermal method coupled with phosphorization treatment. The hierarchical hollow flower-like NPO/NixPy@NF electrodes exhibited high bifunctional activity and stability for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline solutions. The optimized electrode showed low overpotentials of 76 and 240 mV for HER and OER to reach a current density of 10 mA cm-2, respectively. Notably, the NPO/NixPy@NF electrode only required a low voltage of 1.99 V to reach the current densities of 100 mA cm-2 with long-term stability for overall water splitting using the NPO/NixPy@NF|| NPO/NixPy@NF cell, surpassing that of the Pt/C-RuO2 (2.24 V@ 100 mA cm-2). The good catalytic and battery performance should be attributed to i) the open hierarchical structure that enhanced the mass transfer; ii) a highly conductive substrate that accelerated the electron transfer; iii) the rich heterojunction and strong synergy between Ni2P and Ni5P4 that improved the catalytic kinetic; iv) the proper-thickness amorphous phosphorus oxide nitride (PON) shell that realized the stability. This work demonstrates a promising methodology for designing bifunctional transition metal phosphides with high performance for efficient water splitting.

Carbon Nanotubes-Based Fuel Cell for Cr(VI) Removal and Electricity Generation.

A fuel cell, an energy transducer, can convert chemical energy into electrical energy. In this work, graphite felt (GF) loaded with polypyrrole (PPy) and carboxylic carbon nanotubes (CNTs-COOH) was used as a cathode (GF/PPy/CNTs-COOH) in a double-chamber nonbiofuel cell (D-nBFC) to remove Cr(VI) efficiently. Therein, Na2S2O3 in an alkaline solution and Cr(VI) in a strongly acidic solution were employed as anode and cathode solutions, respectively. An agar salt bridge, consisting of saturated KCl solution, was used to transport ions between the anode and cathode. This system suggested that the removal efficiency of Cr(VI) could reach 99.6%. The maximum current, power, and power density could achieve 136.8 µA, 18.7 µW, and 20.8 mW/m2 at 90 min, respectively. Additionally, GF/PPy/CNTs-COOH also had good electrocatalytic stability and reusability after four cycles, which played an important role in the development of the D-nBFC system. Therefore, this study provides an environmentally friendly and efficient method to remove Cr(VI) and generate electricity simultaneously.

Surface Phosphorus-Induced CoO Coupling to Monolithic Carbon for Efficient Air Electrode of Quasi-Solid-State Zn-Air Batteries.

One challenge facing the development of air electrodes for Zn-air batteries (ZABs) is the embedment of active sites into carbon, which requires cracks and blends between powder and membrane and results in low energy efficiency during manufacturing and utilization. Herein, a surface phosphorization-monolithic strategy is proposed to embed CoO nanoparticles into paulownia carbon plate (P-CoO@PWC) as monolithic electrodes. Benefiting from the retention of natural transport channels, P-CoO@PWC-2 is conducive to the construction of three-phase interface structure for efficient mass transfer and high electrical conductivity. The electrode exhibits remarkable catalytic activities for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) with a small overpotential gap (EOER - EORR  = 0.68 V). Density functional theory calculations reveal that the incorporation of P on P-CoO@PWC-2 surface adjusts the electronic structure to promote the dissociation of water and the activation of oxygen, thus inducing catalytic activity. The monolithic P-CoO@PWC-2 electrode for quasi-solid-state or aqueous ZABs has excellent specific power, low charge-discharge voltage gap (0.83 V), and long-term cycling stability (over 700 cycles). This work serves as a new avenue for transforming abundant biomass into high-value energy-related engineering products.

Wood-Derived Integral Air Electrode for Enhanced Interfacial Electrocatalysis in Rechargeable Zinc-Air Battery.

Zinc-air batteries (ZABs) are promising as energy storage devices owing to their high energy density and the safety of electrolytes. Construction of abundant triple-phase boundary (TPB) effectively facilitates cathode reactions occurring at TPB. Herein, a wood-derived integral air electrode containing Co/CoO nanoparticles and nitrogen-doped carbonized wood (Co/CoO@NWC) is constructed with a dual catalytic function. The potential gap between oxygen reduction and evolution is shortened to 0.77 V. Liquid ZABs using Co/CoO@NWC as cathode exhibit high discharge specific capacity (800 mAh gZn-1 ), low charge-discharge gap (0.84 V), and long-term cycling stability (270 h). Co/CoO@NWC also shows distinguished catalytic activity and stability in all-solid-state ZABs. The inherent layered porous and pipe structures of wood are well maintained in catalytically active carbon. The different hydrophilicity of carbonized wood and Co/CoO endow abundant TPBs for battery reaction. The Co/CoO located on TPB provides main active sites for oxygen reactions. The inherent pipe structures of wood carbon and the interaction between Co/CoO and NWC effectively prevent nanoparticles from aggregation. The design and preparation of this monolithic electrocatalyst contribute to the broad-scale application of ZABs and promote the development of next-generation biomass-based storage devices.