Boosted electrolytic hydrogen production at tailor-tuned nano-dendritic Ni-doped Co foam-like catalyst

Ni,S co-doped Cu dendrites decorated with core-shell architecture assisted by MOF and Fe0.92Co0.08S nanoflakes on nanocellulose/graphene fibers for fabrication of flexible wire-type micro-supercapacitor

One-dimensional micro-supercapacitors (1D micro-SCs) have been regarded as an efficient energy storage system to fulfill the ever-growing need for miniaturized electronics. Designing multi-dimensional nanoarchitectures on fibrous microelectrodes is an effective strategy to build a high-performance 1D micro-SC. In this work, Ni,S-doped Cu was firstly prepared on Cu wire as a micro-sized 1D current collector through Cu electrodeposition using a H2 bubble template and then co-doped with nickel and sulfur. Benefiting from the high electrical/thermal conductivity of Cu, and the highly electroactive sites of Ni and S as well as the 3D porous architecture, the deposited Ni,S-doped Cu provided a platform for growing active substances. Thereafter, cobalt carbonate hydroxide (CoCH) pine-like nanoneedle integrated ZIF-67 polyhedrons were synthesized on a foam-like skeleton and converted into NiMoCo-layered triple hydroxide (LTH)/Ni,S-doped Cu shish-kebab type nanoarrays by applying a hydrothermal method. Finally, Ni2Mo3N-CoN/Ni,S-doped Cu was prepared via nitridation. The potent interactions and synergy between components realized a well-organized hybrid nanoarchitecture consisting of dodecahedrons decorated on needle-like arrays within a 3D framework with rich redox properties, rapid ion/electron transfer dynamics and high electroactivity. In comparison to the LTH obtained from the electrodeposition method (without the ZIF-67 precursor) and that derived from leaf-like ZIF-Co, this modified microfiber exhibited a high charge storage capacity of 1.5 mA h cm-2 (149.9 mA h cm-3 and 0.187 mA h cm-1) at 4 mA cm-2 and possesses an excellent durability of 98.4% after 5000 cycles. Additionally, FeCoS nanoflakes were electrodeposited using carbon fiber coated with an rGO-nanocellulose hydrogel (GNCH) and employed as a negative 1D microelectrode, which delivered a high specific capacitance of 1223 mF cm-2 (83 F cm-3, 232.4 mF cm-1) at 4 mA cm-2 with a superior cyclic lifespan. Ultimately, the assembled 1D flexible micro-device (Ni2Mo3N-CoN/Ni,S-doped Cu@CW//FeCoS/GNCH@CF) yielded an energy density of 7.2 mW h cm-3 at a power density of 294 mW cm-3 and outstanding cycling stability in PVA/KOH electrolyte and preserved the capacitive performance under various bending states. This research highlights that assembled 1D micro-SCs have a high potency for next-generation portable/wearable energy-supply microelectronics.

Promoted glucose electrooxidation at Ni(OH)2/graphene layers exfoliated facilely from carbon waste material

Nowadays, the glucose electro-oxidation reaction (GOR) is considered one of the most important solutions for environmental pollution. The GOR is the anodic reaction in direct glucose fuel cells and hybrid water electrolysis. In this study, the GOR is boosted using a carbon support modified with Ni(OH)2 as a non-precious catalyst. The carbon support, with in situ generated graphene nanosheets having a large surface area, grooves, and surface functional groups, is prepared via a simple electrochemical treatment of the carbon rods of an exhausted zinc-carbon battery. Ni(OH)2 is electrodeposited on the surface of the functionalized exfoliated graphite rod (FEGR) via the dynamic hydrogen bubbling technique (DHBT) and tested for GOR. The thus-prepared Ni(OH)2/FEGR electrode is characterized by SEM, mapping EDX, HR-TEM, XRD, and XPS characterization tools. Ni(OH)2/FEGR displays an onset potential of 1.23 V vs. the reversible hydrogen electrode (RHE) and attains high current densities at lower potentials. Additionally, Ni(OH)2/FEGR showed prolonged stability toward GOR by supporting a constant current over a long electrolysis time. The enhanced catalytic performance is attributed to the superb ionic and electronic conductivity of the catalyst. Importantly, ionic conductivity increased, due to (i) a large surface area of in situ generated graphene layers, (ii) enhanced distribution of active material during deposition using DHBT, and (iii) increased hydrophilicity of the underlying substrate. Therefore, the Ni(OH)2/FEGR electrode can be used efficiently for GOR as a low-cost catalyst, achieving low onset potential and high current densities at low potentials.

Copper dendrite stabilized NiFe(OH)x electrocatalyst for durable alkaline hydrogen evolution over 1000 h

Durable Cu/NiFe(OH)_x electrocatalyst was designed for hydrogen evolution reaction in alkaline media. The in situ generated Cu nanodendrites protect the NiFe(OH)_x from being hydrogenated, giving it a > 1000 h lifetime for high-performance water splitting (1.51 V, 10 mA cm^-2 in 1 M KOH) when coupled with a NiFe-layered double hydroxide anode.