The effect of the carbon components on the performance of carbon-based transition metal electrocatalysts for the hydrogen evolution reaction

Abstract

The hydrogen evolution reaction (HER) is a promising way to produce hydrogen, and the use of non-precious metals with an excellent electrochemical performance is vital for this. Carbon-based transition metal catalysts have high activity and stability, which are important in reducing the cost of hydrogen production and promoting the development of the hydrogen production industry. However, there is a lack of discussion regarding the effect of carbon components on the performance of these electrocatalysts. This review of the literature discusses the choice of the carbon components in these catalysts and their impact on catalytic performance, including electronic structure control by heteroatom doping, morphology adjustment, and the influence of self-supporting materials. It not only analyzes the progress in HER, but also provides guidance for synthesizing high-performance carbon-based transition metal catalysts.

1. Introduction

Hydrogen is an important chemical raw material and a clean fuel. Producing hydrogen through water splitting by utilizing renewable energy is a promising technology[1]. Efficient electrocatalysts are usually applied in water splitting to promote the hydrogen evolution reaction (HER). However, most of the efficient electrocatalysts reported in the literature are still composed of precious metals (Pt/C[2,3]), which have poor prospects of practical viability due to low availability of reserves and high cost[4]. Therefore, developing non-precious metal-based materials with outstanding electrochemical performance is of great significance.

In recent years, a lot of electrocatalytic materials covering transition metal sulfides, carbides, phosphides, selenides, oxides, etc. have been developed as HER electrocatalysts with high performance, excellent stability and low price[5,6]. Although transition metal catalysts have high HER catalytic activity, their low conductivity and poor stability require further structural optimization[7].

In recent years, new carbon nanomaterials such as graphene, carbon nanotubes, and porous carbon with large specific surface area, favorable stability and excellent conductivity have emerged continuously[8]. These carbon materials have been combined with various transition metal catalysts for application in HER, and good catalytic performance has been achieved[9,10]. The methods to improve the activities of electrocatalysts can be divided into 2 categories: (1) To enhance the intrinsic reactivity of active center through component adjustment[11]. (2) To increase the number of active sites through structural regulation, thereby increasing the apparent activity[12]. Combining carbon materials with various non precious metal catalysts to form carbon-based transition metal catalysts can simultaneously achieve the above two strategies[13,14]. Carbon-based transition metal catalysts are a new types of catalysts in which transition metals are loaded onto carbon materials. They are usually synthesized by high-temperature carbonization of carbon material precursors and transition metal salts. The chemical composition of carbon materials and various transition metal salts, as well as the binding modes between different components, are highly adjustable, which enable the adsorption and desorption of catalysts with reactants and reaction intermediates to be regulated, facilitating the optimization of intrinsic activity[11]. On the other hand, when carbon materials are served as substrate, active substances are loaded onto the pores/channels, inner and outer surfaces, internal cavities, or encapsulated within the main framework of carbon materials, forming composite catalysts[15]. In this composite structure, the carbon material serves as a physical carrier, serving as both a conductive network and a surface modifier to enhance the adsorption and desorption ability of reactants and active substances.