Phosphazene-Based Covalent Organic Polymer Decorated with NiCo₂O₄ Nanocuboids as a Trifunctional Electrocatalyst: A Unique Replacement for the Conventional Electrocatalysts

Abstract

Developing nonprecious metal-based electrocatalysts to convert water into green fuels (H2 and O2) is key to address urgent climate and energy challenges. We have prepared an electrocatalyst by the immobilization of NiCo2O4 on a phosphazene-based covalent organic polymer (P-COP) through a facile hydrothermal method. The elemental composition of the P-COP showed the presence of a greater amount of heteroatoms N (6.62%) and P (5.62%) throughout the polymer support. Scanning transmission electron microscopy (STEM) and electron energy loss spectroscopy (EELS) were utilized to determine the atomic structure of the nanocuboids, which depicted the formation of an inverse spinel structure. A NiCo2O4-P-COP-based electrode was simultaneously used for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), and it displayed a minimum overpotential of 270 and 130 mV (V vs RHE), respectively, at a current density of 10 mA cm–2. In addition, it acted as an oxygen reduction catalyst with a half-wave potential of 0.83 V (V vs RHE) and a maximum current density of 4.5 mA cm–2. The electrocatalytic activity is comparable with that of the commercially available Pt and RuO2 catalysts. The combined experimental and computational studies confirm that the catalytic centers formed through the interaction between the heteroatoms (N and P) in the phosphazene matrix and metal oxides (Co and Ni) play an important role in its improved durability and electrocatalytic activity.

Phosphazene Cyclomatrix Network-Based Polymer: Chemistry, Synthesis, and Applications

“… Schematic illustration of the synthesis of the P-COP and NiCo 2 O 4 -P-COP (a), TEM images of NiCo 2 O 4 -P-COP (b), and OER, HER, and ORR mechanisms for NiCo 2 O 4 -P-COP (c). 107 Reprinted (adapted) with permission from ref ( 107 ). Copyright (2021) American Chemical Society …”

“…In recent days, carbon materials have attracted the attention of researchers. In particular, porous carbon materials possess a good pore volume with high surface area, extraordinary mechanical stability with less density, and excellent surface permeability with chemical inertness. − These highly noteworthy morphological and structural properties make porous materials very suitable candidates for adsorbents, storage materials, catalyst supports, supercapacitors, and sensors and in solar cells and fuel cells to act as an electrocatalyst for the oxygen evolution reaction (OER), hydrogen evolution reaction (HER), and oxygen reduction reaction (ORR). ,− The cyclopolyphosphazene material pyrolysis has improved their morphological properties from being even on the surface to porous, rigid solid, to hollow and from traditional PN ̵bond to̵ C–C ̵graphitic bond networks in nature . Dufek and co-workers synthesized the PZS and carbonized them at 1000 °C to form porous carbon materials and used lithium ion electrodes which exhibited the stable capacity of 1200 mAh g –1 , with almost 95% retention after 40 cycles …”

“…In addition, it acted as an oxygen reduction catalyst with a half-wave potential of 0.83 V (V vs RHE) and a maximum current density of 4.5 mA cm −2 (Figure 10). 107 5.4. Adsorbent of Toxic Compounds.…”

NIR Photothermal-Enhanced Electrocatalytic and Photoelectrocatalytic Hydrogen Evolution by Polyaniline/SnS2 Nanocomposites

“…To achieve these targets, one of the most direct and important ways is reducing the usage of fossil fuels and increasing the application of clean and sustainable energy sources. − As a zero-carbon energy storage carrier, hydrogen (H 2 ) is the desired fuel with a high calorific value for the future. Therefore, the development of H 2 production methods has great significance and is becoming an increasingly important and interesting research topic nowadays. − Electrochemical water splitting (EWS) is regarded as one of the most effective methods for hydrogen evolution. − To overcome the drawbacks of EWS (high overpotential and electricity consumption), suitable catalysts are required to reduce the reaction activation energy and speed up the kinetics of producing H 2 . − In addition, combined strategies including light- and photothermal-enhanced electrochemical water splitting have attracted particular attention, , which would be potential approaches for sustainable and more efficient H 2 evolution. The synergistic effects between light/heat and electronic fields can promote charge separation rate, reduce energy consumption, and improve electrocatalytic or photocatalytic performance .…”

“…The synergistic effects between light/heat and electronic fields can promote charge separation rate, reduce energy consumption, and improve electrocatalytic or photocatalytic performance . Therefore, finding efficient, stable, cheap, environmentally friendly electrocatalysts with low Gibbs adsorption energy for H 2 is in great demand. − …”