Co_xP@Co₃O₄ Nanocomposite on Cobalt Foam as Efficient Bifunctional Electrocatalysts for Hydrazine-Assisted Hydrogen Production

Abstract

The kinetically sluggish oxygen evolution reaction (OER) at an anode has always been the bottleneck in the largescale application of electrocatalytic water splitting to produce ecofriendly and sustainable hydrogen. Therefore, replacing the OER with hydrazine oxidation reaction (HzOR), which requires a lower theoretical potential, has been considered as a more energyefficient strategy. Herein, a novel bifunctional Co x P@Co 3 O 4 nanocomposite with grass-like and block-like structures was fabricated on Co foam (defined as P−Co 3 O 4 /Co) via a facile hydrothermal synthesis for Co 3 O 4 and the sodium hypophosphitephosphorization method for cobalt phosphides. Compared with the Co 3 O 4 precursor on Co foam, the heterogeneous P−Co 3 O 4 / Co, composed of a mixture of CoP, Co 2 P, and Co 3 O 4 , possessed superb electrochemical catalytic activity for both the hydrogen evolution reaction and HzOR in 1.0 M KOH and 0.3 M hydrazine medium. Low overpotentials of 106 and 129 mV were required to deliver current densities of 10 and 200 mA cm −2 , respectively. Meanwhile, potentials of −100 and −83 mV are needed to drive current densities of 10 and 200 mA cm −2 , respectively, which exceed those of almost recently reported catalysts. The excellent performance can be attributed to the fact that the synergistic effect between the presence of multiphase of Co x P/Co 3 O 4 and the three-dimensional porous Co foam substrate makes the as-synthesized catalyst possess a large specific surface area and fast charge/ mass transport. Density functional theory calculations unravel that the phosphorization strategy can not only regulate the electronic structure of pristine Co 3 O 4 , enhancing the electronic conductivity, but also optimize the adsorption/desorption strength of H* and alter the free energy change of the dehydrogenation kinetics of NH 2 NH 2 *. Meanwhile, a low cell voltage of 1 V was achieved to deliver a current density of 948 mA cm −2 when P−Co 3 O 4 /Co behaved as both the cathode and anode simultaneously, which was superior to most of the nonprecious metal-based catalysts.

Dopamine‐Assisted Coral Films of Cobalt as Bifunctional Electrodes for Overall Water Splitting

“…The peak at 796.6 and 780.6 eV suggests the existence of Co 3+ , whereas 797.8 and 782.4 eV correspond to Co 2+ , which agrees with the previous reports. [ 50 ] The deconvoluted peaks in the spectrum at 795.6 and 779.7 eV are due to Co 0 2 p 1/2 and 2 p 3/2 , respectively; these values match well with the values that are reported in the literature. [ 51 ] In addition, the spectrum also consists of satellite signals around 785 and 802 eV, indicating the slight surface oxidation of Co. As the signal in XPS technique prominently comes from the upper surface of the samples, the oxidation states Co 2+ and Co 3+ are more pronounced than the metallic Co 0 state.…”

Vanadium-Doping and Interface Engineering for Synergistically Enhanced Electrochemical Overall Water Splitting and Urea Electrolysis

“…Recently, as an alternative to traditional hydrogen production from electrocatalytic water splitting, many readily oxidizable molecules including alcohols, glucose, urea, , hydrazine, , and 5-(hydroxymethyl)­furfural , have been deployed to replace the OER process in order to improve the energy efficiency. As one of these molecules, the thermodynamic potential of the urea electro-oxidation reaction (UOR) is 0.37 V (CO­(NH 2 ) 2 + 6OH – → N 2 + CO 2 + 5H 2 O + 6e – ), much less than 1.23 V of OER. , Therefore, UOR is a thermodynamic favorable process.…”

A Zeolitic-Imidazole Framework-Derived Trifunctional Electrocatalyst for Hydrazine Fuel Cells

“…Rising global energy demands have eventually evoked concerns for sustainable energy conversion technologies. − Hence, alternate energy resources that do not rely on fossil fuels are receiving enormous consideration. Among the different renewable energy sources, hydrazine fuel cells are promising due to their high theoretical power density. − Nevertheless, the slow reaction kinetics and limited diffusion properties of electrochemical reactions involved in the hydrazine fuel cells hinder their desired cell performances. − Therefore, optimizing the reaction kinetics by rational design of electrocatalysts and constructing efficient cell configurations is indispensable to step up their application in hydrazine fuel cells. − By far, some precious-metal-based electrocatalysts have exhibited outstanding activities in the hydrazine fuel cells, yet large-scale applications are still severely hindered by their limited reserves and high price. , …”