Synthesis of P-(NiCo)CO3 /TiO2 /Ti Self-Supported Electrode with High Catalytic Activity and Stability for Hydrogen Evolution.

Hydrogen is considered an ideal clean energy due to its high mass-energy density, and only water is generated after combustion. Water electrolysis is a sustainable method of obtaining a usable amount of pure hydrogen among the various hydrogen production methods. However, its development is still limited by applying expensive noble metal catalysts. Here, the dissolution-recrystallization process of TiO2 nanotube arrays in water with the hydrothermal reaction of a typical nickel-cobalt hydroxide synthesis process followed by phosphating to prepare a self-supported electrode with (NiCo)CO3 /TiO2 heterostructure named P-(NiCo)CO3 /TiO2 /Ti electrode is combined. The electrode exhibits an ultra-low overpotential of 31 mV at 10 mA  cm-2 with a Tafel slope of 46.2 mV dec-1 in 1 m KOH and maintained its stability after running for 500 h in 1 m KOH. The excellent catalytic activity can be attributed to the structure of nanotube arrays with high specific surface area, superhydrophilicity, and super aerophobicity on the electrode surface. In addition, the uniform (NiCo)CO3 /TiO2 heterostructure also accelerates the electron transfer on the electrode surface. Finally, DFT calculations demonstrate that phosphating also improves the ΔGH* and ΔGH2O of the electrode. The synthesis strategy also promotes the exploration of catalysts for other necessary electrocatalytic fields.

Highly selective and sensitive nitrite biocathode biosensor prepared by polarity inversion method coupled with selective removal of interfering electroactive bacteria.

Nitrite is a multipurpose marker that needs to be detected quickly and accurately, including for water pollution and human urinary tract infections. In this study, we reported a novel nitrite-reducing bacteria electrochemical biosensor based on the metronidazole-treated biocathode (MT-NBEB). The biocathode with high nitrite response sensitivity used was first prepared by polarity inversion method and then treated with metronidazole to selectively remove the interfering electroactive bacteria for selectivity improvement. MT-NBEB could detect nitrite in the range of 0.0001 mg NO2--N L-1-8 mg NO2--N L-1 within 1.7 min and maintain stable detection performance for over 50 continuous cycles with relative standard deviations < 2.4%. Besides, the response signals of MT-NBEB were not affected by the common inorganic salts (such as nitrate and ammonia) and organic matter (such as acetate). MT-NBEB successfully detected nitrite in five types of wastewaters with relative errors < 14.3%. Our study provided a feasible way to prepare highly selective and sensitive electrochemical biosensors to quickly and accurately detect nitrite in real wastewaters.

Modifying Ti3C2 MXene with NH4+ as an excellent anode material for improving the performance of microbial fuel cells.

Poor anode performance is one of the main bottlenecks in the development of microbial fuel cells (MFCs) for practical applications. Multilayered Ti3C2 MXene (m-MXene) is an alternative anode modification material because of its high specific surface area and electrical conductivity. However, the multilayered structure, negatively charged surface, and electropositivity of m-MXene could limit its modification effects. In this work, we used a solution-phase flocculation method (ammonium ion method) to restack and aggregate MXene nanosheets as an anode modification material (n-MXene). The n-MXene-modified anode had a higher specific surface area, surface hydrophilicity and surface electropositivity than the m-MXene-modified anode. The n-MXene-modified anode obtained a maximum current density of 2.1 A m-2, which was 31.2% and 61.5% higher than that of the m-MXene-modified anode (1.6 A m-2) and bare carbon fiber cloth anode (1.3 A m-2). This improved anode performance was attributed to both the decrease in the charge transfer resistance and diffusion resistance, which were related to the increased quantity of biomass and microbial nanowire (or pili)-shaped filaments on the electrode surface. This work provides a simple and cost-effective approach to prepare MXene nanosheets for the modification of MFC anodes.

Efficient degradation of polyacrylamide using a 3-dimensional ultra-thin SnO2-Sb coated electrode.

Polyacrylamide (PAM) is widely used in polymer flooding processes to increase oil recovery while the byproduct of PAM-containing wastewater is a serious environmental issue. In this study, electrochemical oxidation process (EAOP) was applied for treating PAM wastewater using a new type of 3-dimensional ultra-thin SnO2-Sb electrode. Nano-sized catalysts were evenly dispersed both on the surface and inside of a porous Ti filter forming nano-thickness catalytic layer that enhances the utilization and bonding of catalysts. This porous Ti electrode showed 20% improved OH· production and 16.3 times increased accelerated service life than the planar Ti electrode. Using this electrode to treat 100 mg L-1 PAM, the TOC removal efficiency reached over 99% within 3 h under current density of 20 mA cm-2. The EAOP could fastly break the long-chain PAM molecules into small molecular intermediates. With the porous electrode treating 5 g L-1 PAM under current density of 30 mA cm-2, EAOP reduced 94.2% of average molecular weight in 1 h and 92.0% of solution viscosity in 0.5 h. Moreover, the biodegradability of PAM solution was significantly improved as the solution BOD5/COD ratio raised from 0.05 to 0.41 after 4 h treatment. The degradation pathway of PAM was also investigated.