Spatially dispersed one-dimensional carbon architecture on oxide framework for oxygen electrochemistry

The rational design of bifunctional electrocatalyst is important for sustainable energy storage and conversion devices such as metal-air batteries and fuel cells. Herein, we have designed a unique architecture where carbon nanotubes (CNTs) are supported on an oxide template. NiCo encapsulated N-doped carbon nanotubes were grown vertically outward from the nickel–cobalt oxide flowers for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). The hybrid shows enhanced water oxidation performance (321 mV at 10 mA/cm2) and decent ORR activity (E1/2 at 0.75 V vs RHE) due to better conductivity and a large electrochemical surface area. Enhanced OER activity can be ascribed to high Ni and Ni3+ content whereas improved ORR activity results from enhanced active nitrogen species (pyridinic, M−Nx and graphitic) and higher water contact angle (due to unique architecture). Further, reversible oxygen electrochemistry with Δ E = 0.80 V indicates its potential as a bifunctional electrocatalyst. The hybrid electrocatalyst has shown good operational stability and durability for OER and ORR. Finally, the practical feasibility as cathode catalyst for metal-air battery has been demonstrated by powering a light emitting diode.Ministry of Education (MOE)Submitted/Accepted versionThe authors gratefully acknowledge DST-FIST (SR/FST/PSII-009/2010), India and Ministry of Education, Singapore (RG15/16, RG16/18) for the financial support

Trimetallic oxide-hydroxide porous nanosheets for efficient water oxidation

Multimetallic systems have been the subject of intensive research for their promising electrocatalytic activities. Herein, we describe the synthesis of bimetallic and trimetallic (Ni, Co and Mn) oxide-hydroxide nanosheets and evaluate their catalytic activity toward water oxidation. The catalytic activity of porous trimetallic nanosheets was found to be higher than that of bimetallic hybrids. In addition, the trimetallic systems also possess excellent stability. A current density of 10 mA/cm2 is achieved for an overpotential of 287 mV and ∼0% loss even after 8000 cycles. The enhanced performance by the trimetallic system can be attributed to the large electrochemical surface area and better intrinsic activity. The electronic modulation in this three-element system is evident from the X-Ray Photoelectron Spectroscopy (XPS) study and Mott-Schottky analysis. The position of flat-band potential plays a significant role in determining the charge transfer kinetics, thereby affecting the water oxidation activity in the semiconductor-electrolyte system. Trimetallic system also offers better oxygen evolution reaction kinetics as evident from the least activation energy compared to the bimetallic counterparts. The local structure system is realized with the X-ray absorption spectroscopy (XAS) analysis. The present study highlights the importance of intrinsic activity in designing efficient non-noble metal electrocatalysts.Ministry of Education (MOE)Submitted/Accepted versionThe authors gratefully acknowledge DST-FIST (SR/FST/PSII-009/2010), India and Ministry of Education, Singapore (RG15/16, RG16/18) for the financial support

Insights into improving photoelectrochemical water-splitting performance using hematite anode

Designing an efficient photoanode is of great importance for photoassisted solar water splitting. Herein, a series of modifications to a nanorod structure hematite, to be used as anode for photoelectrochemical (PEC) water-splitting reactions is designed. Ti doping, oxygen vacancy formation by N2 treatment, TiO2 passivation, and FeOOH cocatalyst decoration are explored for their roles and contributions to the improvement of the PEC water oxidation performance. It is found that Ti doping and N2 treatment can greatly increase the charge carrier density, which has boosted the photocurrent. TiO2 passivation enhances the photovoltage, resulting in a cathodic shift in the onset potential (≈170 mV with respect to prepassivation). Further, the FeOOH cocatalyst decoration improves the reaction kinetics, thereby improving the overall photoassisted water oxidation performance.Ministry of Education (MOE)Submitted/Accepted versionThe authors gratefully acknowledge DST-FIST, India (SR/FST/PSII-009/2010), and Ministry of Education, Singapore (RG15/16, RG16/18), for financial support