Developments in electrocatalysts for electrocatalytic hydrogen evolution reaction with reference to bio-inspired phthalocyanines

The increasing global energy demand has resulted in consumption of fossil fuel-based resources at a rapid rate. This has led to depletion of the fossil fuels at a faster rate and in addition, the toxic gases produced on burning of fossil fuels have caused a serious impact on environment. Owing to the fulfillment of energy demand for sustainable development, it is of paramount importance to focus and develop renewable energy sources as major energy supply chain. Hence, lot of efforts has been put in the develop-ment of environment friendly, safe, cost-effective, and reliable renewable energy storage and conversion systems. Among the various alternative energy systems, the electro-chemical energy devices like proton exchange membrane fuel cells are of major concern as they provide continuous energy with high energy density, easy transportation, portable devices with clean and green energy. These Fuel cells need a fuel and an oxidant to produce the electrical energy. The molecular hydrogen (H2) is a prominent clean and green renewable energy source which is used as an efficient fuel in fuel cell devices. Out of various methods of H2 production, water splitting reaction has clinched much attention as it is an efficient method for H2 production and does not involve the release of any carbon footprints to atmosphere. However, the sluggish kinetics of hydrogen evolution reaction (HER) at the cathode is one of the major limitations in water electrolyzer and in addition, precious and less abundant Pt is employed as catalyst at cathode which hinders the commercialization of the fuel cells. In this context, the design and development of effi-cient, cost effective and durable electrocatalyst material for HER is a biggest challenge. Among the various types of catalytic materials, N-4 macrocycle derived catalysts namely, phthalocyanines have been recognized as potential cathode electrocatalysts for improving the reaction kinetics of the HER. This review highlights the advantages of phthalocyanine based catalysts over other metal-based catalysts and presents recent developments in MPc based electrocatalysts for the HER. The review gives brief introduction to the fundamentals and reaction mechanism of HER activity. The dependence of HER activity on the electrolyte and pH are discussed. An elaborative description has been provided on different kinds of electrocatalysts employed for HER including noble metal catalysts and non-precious as well as carbon based elec-trocatalysts. Furthermore, an emphasis has been provided on the N-4 macrocycles, particularly MPc based materials including introduction to MPcs, potential properties and advantages for HER activity. Various experimental parameters like catalytic activity and long-term stability of the MPc based electrode materials have been considered. At the end, summary and outlook as well as future challenges of MPc complex materials have been discussed. (c) 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

The increasing global energy demand has led to rapid consumption of fossil fuel-based resources, resulting in depletion of fossil fuels and serious environmental impact from toxic gas emissions. To meet sustainable development goals, it is crucial to focus on and develop renewable energy sources. Among these, proton exchange membrane fuel cells, which use molecular hydrogen as a fuel, are of great importance due to their continuous energy supply, high energy density, and clean characteristics. However, the sluggish kinetics of the hydrogen evolution reaction at the cathode and the use of precious and less abundant platinum as a catalyst hinder the commercialization of these fuel cells. Phthalocyanine-based catalysts, particularly N-4 macrocycles, have shown potential in improving the reaction kinetics of the hydrogen evolution reaction. This review highlights the advantages of phthalocyanine-based catalysts and presents recent developments in their application for the hydrogen evolution reaction, discussing various experimental parameters and long-term stability.