N-doped mixed Co, Ni-oxides with petal structure as effective catalysts for hydrogen and oxygen evolution by water splitting.

Developing electrocatalytic nanomaterials for green H2 energy is inseparable from the exploration of novel materials and internal mechanisms for catalytic enhancement. In this work, nano-petal N-doped bi-metal (Ni, Co) and bi-valence (+2, +3) (Ni1-x Co x )2+Co2 3+O4 compounds have been in situ grown on the surface of Ni foam. The N3- atoms originate from the amino group in urea and doped in the compound during annealing. The as-synthesized N-doped (Ni1-x Co x )2+Co2 3+O4 nano-petals demonstrate commendable hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) bi-functional catalytic efficiency and stability. Electrochemical measurements confirm that the nitrogen doping significantly improves the catalytic kinetics and the surface area. Density functional theory calculations reveal that the improved HER and OER kinetics is not only due to the synergistic effect of bi-metal and bi-valence, as well as the introduction of defects such as oxygen vacancies, but also it more depends on the shortened bond length between the nitrogen N3- atoms and the metal atoms, and the increased electron density of the metal atoms attached to the N3- atoms. In other words, the change of lattice parameters caused by nitrogen doping is more conducive to the catalytic enhancement than the synergistic effect brought by bi-metal. This study provides an experimental and theoretical reference for the design of bi-functional electrocatalytic nanomaterials.

ZnFe2O4 Nanotapers: Slag Assistant-Growth and Enhanced Photoelectrochemical Efficiency.

In this study, ZnFe2O4 (ZFO) nanotapers are fabricated on the ZnO nanorods (NRs) by recycling rare-earth oxide (REO) slag as the iron source, which thereby exhibits dramatically enhanced photoelectrochemical (PEC) efficiency. Our studies demonstrate that the electron-hole separation and charge migration can be facilitated by the cascade band alignment of ZFO and ZnO and the branched nanotaper structures. Not only the iron source, the slag particles can also act as the passivation layers, leading to improved electron lifetime and significant PEC enhancement. The current study presents a novel REO-slag-modified PEC anode for high-efficiency PEC devices and offers a possibility of recycling industrial waste for renewable energy generation.