Exploration of Ni-P-Based Catalytic Electrodes for Hydrogen Evolution Reaction

Introduction

Hydrogen Fuel Cell Technology, for stationary application can be the best potential for Hydrogen energy with maximum energy efficiency but minimum or no environmental issues. Hydrogen, the fuel used in this technology should be continuously propelled to the cell for continuous energy production. This chapter aims to provide understanding of scientific aspects of hydrogen production techniques and the enhancement techniques especially by suitable catalyst material design and implementation. The thorough knowledge of the aspects mentioned here will realize the enhanced hydrogen production for Hydrogen Fuel Cell Technology for stationary application. Electrocatalytic hydrogen evolution is considered as an effective and sustainable technique to convert electric energy to chemical energy. Hydrogen Evolution Reaction (HER) is regarded as the main step in electrochemical water splitting and the foundation for discovering the mechanism of many supplementary multi–electron transfer electrochemical phenomena. The experimental set up for electrochemical water splitting comprises of a Direct Current (DC) power source electrically connected to two electrodes, i.e. an anode and a cathode (with electrocatalysts) immersed in water. Hydrogen and oxygen are evolved from the cathode and anode respectively. Generally, for a water–splitting reaction to begin, excess energy as overpotential is required to overcome several activation barriers. If not, the reaction either won’t happen or may occur at a relatively lower rate, which is due to the poor self-ionization power of water. However, efficacy of the reaction can be increased by: adding suitable electrolytes as a salt, an acid or a base; and with the usage of appropriate electrocatalysts. Targeting on efficient water splitting on a large scale basis, so far, many electrocatalysts have been developed accompanied by current substantial advances in discovering more on their electrochemical nature. From a fundamental point of view, an electrocatalyst, for better performance, must satisfy the following conditions;

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  For the desired reaction i.e., for HER, the intrinsic overpotential must be low.

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  Surface area of the electrocatalyst must be active enough facilitating good approachability to the reactants and suitably for the fast exclusion of products (Sapountzi et al., 2017)

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  Possess high electrical conductivity so as to provide favorable pathways for electron transfer reactions.

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  Possess chemical stability i.e., it should be compatible with the used electrolyte.

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  Possess electrochemical stability i.e., it should not get corroded at high overpotential.

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  Possess good mechanical stability (applicable at high temperature electrolysis).

All these conditions guarantee high overall system efficiency. Moreover, long term stability and cost effectiveness are also to be focussed to compete with the conventional non sustainable methods.

Electrocatalytic HER is the most widely explored electrochemical reaction in a feasible manner and has wide applications extending from corrosion and electrodeposition of metals to energy storage by means of hydrogen production. Among the various sustainable hydrogen production methods developed, electrocatalytic HER is considered to be the most efficient strategy owing to its supreme capacity and carbon free emission. It has a great benefit of producing extremely pure hydrogen i.e., with purity greater than 99.9%, perfect for some upgraded processes, mainly for the manufacture of electronic components (Pletcher & Li, 2011). Moreover, the theoretical and experimental studies of HER electrocatalysts with special attention on their electronic structure, surface electrochemistry and design need to be evaluated critically.

The idea about basic mechanism of HER, materials development for the same and recent trends in the techniques are very important to be explored, modification of useful systems efficiently and to design novel systems for large scale production. Transition based catalytic systems have shown its significant impact on the research and development in this field. In this context, this review chapter draws attention on scientific aspects of methods and materials used for HER, focusing on its mechanism and Ni based catalytic systems as electrodes which are highly significant for further exploration and industrial applications.