Open-Microcolumn Array: A Novel Approach for Enhanced Electrocatalytic Bubble Desorption in Microreactors

High-efficiency electrocatalytic water splitting requires high intrinsic activity of catalysts and even more importantly favorable mass transfer. However, gas bubbles adhering to the surface of catalysts limit the re-expose of catalytic active sites to the electrolyte and reduce the catalytic activities. The efficient desorption of bubbles can be facilitated by a hierarchical multiscale structure of the electrode surface. Herein, we report an opened periodic three-dimensional electrode composed of iron (Fe)-cobalt (Co)-nickel (Ni) (oxy)hydroxide nanorods (NRs) grown in situ on a high aspect ratio nickel microcolumn array (NCA) for electrocatalytic water splitting. Compared with the flat nickel plate, the NCA not only increases the surface area for catalyst loading but also improves the wettability of the electrolyte on the electrode surface, exhibiting superhydrophilicity/superaerophobicity (the electrolyte and the bubble contact angles were about ∼0 and 163°, respectively), which accelerates the bubble evolution and desorption process. The X-ray photoelectron spectroscopy indicates that the synergy of Fe-Co-Ni could enhance the ratio of Co3+/Co2+ and Ni3+/Ni2+ and promote the electrocatalytic activity. Benefiting from the microstructure design and synergistic effects, the Co4Fe0.5Ni0.5OOH-NR@NCA electrode achieves a superior OER performance with an overpotential of 199 mV at 10 mA·cm-2.

Utilization of nitrogen, sulfur co-doped porous carbon micron spheres as bifunctional electrocatalysts for electrochemical detection of cadmium, lead and mercury ions and oxygen evolution reaction

The development of high-performance bifunctional electrocatalysts for oxygen evolution reaction and heavy metal ion (HMI) detection is significant and challenging. Here, a novel nitrogen, sulfur co-doped porous carbon sphere bifunctional catalyst was designed and fabricated by hydrothermal followed by carbonization using starch as carbon source and thiourea as nitrogen, sulfur source for HMI detection and oxygen evolution reactions. Under the synergistic effect of pore structure, active sites and nitrogen, sulfur functional groups, C-S_0.75-HT-C₈₀₀ demonstrated excellent HMI detection performance and oxygen evolution reaction activity. Under optimized conditions, the detection limits (LODs) of C-S_0.75-HT-C₈₀₀ sensor were 3.90, 3.86 and 4.91 nM for Cd²⁺, Pb²⁺ and Hg²⁺ when detected individually; and the sensitivities were 13.12, 19.50 and 21.19 μA/μM. The sensor also obtained high recoveries of Cd²⁺, Hg²⁺ and Pb²⁺ in river water samples. During the oxygen evolution reaction, a Tafel slope of 70.1 mV/dec and a low overpotential of 277 mV were obtained for C-S_0.75-HT-C₈₀₀ electrocatalyst with a current density of 10 mA/cm² in basic electrolyte. This research offers a neoteric and simple strategy in the design as well as fabrication of bifunctional carbon-based electrocatalysts.

Nitrogen-Doped Oxygenated Molybdenum Phosphide as an Efficient Electrocatalyst for Hydrogen Evolution in Alkaline Media

Phosphides of transition metals (TMPs) are a developing class of materials for hydrogen evolution reaction (HER) as an alternative to expensive noble metals to produce clean energy. Herein, the nitrogen-doped molybdenum oxide (MoOx) is developed via a facile and simple hydrothermal method, followed by annealing in the N2 atmosphere and phosphorization to form a nitrogen-doped oxygenated molybdenum phosphide (N-MoP) sphere-shaped structure. The developed N-doped phosphide structure depicts enhanced HER activity by reaching a current density of 10 mA cm-2 at a very low overpotential of only 87 mV, which is much better than annealed nitrogen-doped molybdenum oxide (A-MoOx) 138 mV in alkaline medium. N-MoP is a highly efficient electrocatalyst for HER attributed to a more exposed surface, large electrode/electrolyte interface and appropriate binding energies for reactants. This study extends the opportunity of developing nitrogen-doped TMPs, which can display exceptional properties as compared to their oxides.

Metal–organic-framework-derived hierarchical Co/CoP-decorated nanoporous carbon polyhedra for robust high-energy storage hybrid supercapacitors

Electrode materials exhibiting nanostructural design, high surface area, tunable pore size, and efficient ion diffusion/transportation are essential for achieving improved electrochemical performance.