Oxygen Vacancy and Core–Shell Heterojunction Engineering of Anemone‐Like CoP@CoOOH Bifunctional Electrocatalyst for Efficient Overall Water Splitting

Abstract

Synthesizing cost-efficient and robust bifunctional electrocatalysts for both neutral and alkaline water splitting is highly desired, but still remains a great challenge due to the sluggish hydrogen/oxygen evolution reaction (HER/OER) kinetics. Currently, noble Pt, Ru, and Ir-based catalysts are the most efficient ones, but their high cost and scarcity greatly restrict their broad applications. [2] Therefore, enormous efforts have been made toward developing suitable and cheaper catalysts with earthabundant materials for commercial applications. In the past years, a large number of non-noble-metal based catalysts, including transition metal phosphides, nitrides, carbides, and oxides, had good development prospects in catalytic fields. [3] Among these, transition metal phosphides (TMPs) such as Fe x P, Co x P, and Ni x P are promising and considered as the most probable alternatives to the noblemetal based catalysts due to their abundant reserves, high stability, non-toxicity, fast charge transfer, and electrical conductivity. [4] However, many studies demonstrated that TMPs exhibited excellent hydrogen evolution reaction (HER) activity (it may be attributed to the reported hydrogenase-like catalytic mechanism), [5] but poor oxygen evolution reaction (OER) activity. So, it is an urgent to improve their catalytic behavior. There are two effective strategies to solve the above problems:Constructing cost-efficient and robust bifunctional electrocatalysts for both neutral and alkaline water splitting is highly desired, but still affords a great challenge, due to sluggish hydrogen/oxygen evolution reaction (HER/OER) kinetics. Herein, an in situ integration engineering strategy of oxygen-vacancy and core-shell heterojunction to fabricate an anemone-like CoP@CoOOH core-shell heterojunction with rich oxygen-vacancies supported on carbon paper (CoP@CoOOH/CP), is described. Benefiting from the synergy of CoP core and oxygen-vacancy-rich CoOOH shell, the as-obtained CoP@CoOOH/CP catalyst displays low overpotentials at 10 mA cm -2 for HER (89.6 mV/81.7 mV) and OER (318 mV/200 mV) in neutral and alkaline media, respectively. Notably, a two-electrode electrolyzer, using CoP@CoOOH/CP as bifunctional catalyst to achieve 10 mA cm -2 , only needs low-cell voltages in neutral (1.65 V) and alkaline (1.52 V) electrolyte. Besides, systematically experimental and theoretical results reveal that the core-shell heterojunction efficiently accelerates the catalytic kinetics and strengthens the structural stability, while rich oxygen-vacancies efficiently decrease the kinetic barrier and activation energy, and reduce the energy barrier of the rate-determiningstep for OER intermediates, thus intrinsically boosting OER performance. This work clearly demonstrates that oxygen-vacancy and core-shell heterojunction engineering provide an effective strategy to design highly-efficient non-precious, bi-functional electrocatalysts for pH-universal water splitting.The ORCID identification number(s) for the author(s) of this article can be found under h...

Boosting Hydrogen Evolution Electrocatalysis via Regulating the Electronic Structure in a Crystalline–Amorphous CoP/CeOx p–n Heterojunction

“…Generally, the heterostructure with a strong interfacial interaction can trigger electron redistribution within the heterointerfaces and consequently modulate the electronic structure and optimize the adsorption energy of intermediates, and even endow the synergistic effect, providing an effective tactic to enhance the intrinsic activity of the active sites. , For instance, the pea-like heterostructured CoP–Mo 2 C incorporated in the N-doped carbon displays a strong synergy and a superior electrocatalytic HER activity . Li and co-workers recently realized the anemone-like oxygen-vacancy-enriched CoP@CoOOH core–shell heterojunction on a carbon paper, exhibiting excellent HER catalytic ability under alkaline and neutral conditions due to the core–shell synergistic effect . Also, other different components, such as Co 3 O 4 , Ni 2 P, and Co 2 P/Co, have also been integrated with CoP to fabricate efficient heterostructured electrocatalysts with advanced electronic structure and electron transport ability. − However, these TMP-based materials are usually synthesized according to complicated growth–phosphorization–modification, growth–secondary growth–phosphorization strategy, or tough hybrid precursor synthesis .…”

Ru/Rh Cation Doping and Oxygen‐Vacancy Engineering of FeOOH Nanoarrays@Ti3C2Tx MXene Heterojunction for Highly Efficient and Stable Electrocatalytic Oxygen Evolution

“…However, it still faces a major challenge, that is, the oxygen evolution reaction (OER) with a four‐electron process (4OH – → O 2 + 2H 2 O + 4e – in an alkaline medium) results in a large overpotential and slow kinetics. [ 1,2 ] Thus, it seriously hinders its large‐scale practical application. So, designing a stable, highly active, and inexpensive electrocatalysts is a key challenge to date.…”

Synergistically Coupled CoMo/CoMoP Electrocatalyst for Highly Efficient and Stable Overall Water Splitting

“…Recently, resource consumption and environmental pollution have seriously hindered sustainable development. − As a new energy source, hydrogen has the advantages of being clean and environmentally friendly with a high calorific value of combustion. − Electrochemical water splitting has received a lot of attention as an ideal technology for the preparation of hydrogen energy. − Although Pt/C and RuO 2 have relatively excellent properties, their low earth reserves and extravagant cost greatly impede their large-scale utilization. − Therefore, the development of high-efficiency catalysts with abundant reserves and moderate price is of great application value but highly challenging. Numerous studies have demonstrated that transition metal compounds, such as nitrides, , selenides, , sulfides, , oxides/hydroxides, , and phosphides, − show great promise in the field of electrocatalysis due to their high hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) performances. In particular, transition metal phosphides (TMPs) are the preferred alternative to noble metals due to their low prices, adjustable valence states, and their ability to improve the adsorption–desorption behavior of the H atoms on material surfaces for high electrocatalytic performance. − In particular, bimetallic phosphide electrocatalysts tend to show better electrochemical activity than monometallic phosphides owing to the strong synergy between the individual components, thus attracting more widespread interest. − Unfortunately, during the electrochemical water-splitting process, the sluggish OER and HER involve different multistep reaction paths and require high activation and dissociation energies of reaction intermediates, thus demanding a catalyst with high performance .…”