**Abstract**

Nanocatalysts for sustainable water electrolysis is strongly desirable to promote the commercialization of H2 as the alternate clean energy source for the future. The goal is cheaper hydrogen production from sea and low grade water by minimizing the energy consumption and using low cost cell components & non-noble metal catalysts. The conductivity of metal nitrides and their ability to carry out Hydrogen Evolution Reaction and Oxygen Evolution Reaction at relatively low overpotential render these one of the frontline candidates to be potentially utilized as the catalyst for low cost H2 production via electrolysis. In this chapter, the potential of metal nitride catalyst towards fulfilling the above objective is discussed. The synthesis of various metal nitride catalysts, their efficiency towards electrode half reactions and the effectiveness of these class of nanocatalyst for electrolysis of sea water is elaborated. A review of recent literature with special reference to the catalyst systems based on non-noble metals will be provided to assess the likelihood of these nanocatalyst to serve as a commercial grade electrode material for sea water electrolysis.

**Keywords:** metal nitride, nanocatalyst, water electrolysis, hydrogel evolution reaction, oxygen evolution reaction

## **1. Introduction**

Low cost, robust alkaline electrolyzers employ non-noble metals as electrodes and allow sustainable electrolysis of water for generation of H2 at a commercial level. The goal is cheaper hydrogen production by minimizing the energy consumption and using low cost cell components. The important factor for consideration here is the use of sea water for H2 generation in the cell environment. Sea-water and ground water are multicomponent natural electrolytes with alkali chloride as the main component. However, the major issue with such water electrolysis is the production of toxic chlorine gas (Cl2) at the anode along with O2 gas. Oxygen evolution reaction (OER) involves a four electron transfer, which makes it much more difficult to catalyze compared to the chlorine evolution reaction (CER), where only a two electron transfer is involved. There have been several attempts to suppress CER during saline water electrolysis such as use of special catalysts that favor OER over CER, coating the anode with protective layers to prevent it from adsorption of chloride ion, and salting out NaCl from the electrolyte solution. Another problem of using sea water or high TDS water is the precipitation of hydroxides of magnesium and calcium on electrode surfaces due to alkaline nature of cathode. Removal of calcium and magnesium prior

to electrolysis involve additional cost and generation of solid wastes. Therefore, prevention of precipitation of hydroxides is necessary to run the electrolyzer smoothly for a long period. Recent studies show that formation of Mg2+ and Ca2+ precipitate on the electrode can be overcome by operating the electrolyzer at near neutral pH, which would also enable the use of low cost earth-abundant electrocatalysts.
