Metal-Free Catalysts for Hydrogen Production

Abstract

Catalysts are vital for speeding up the reaction during hydrogen production. Both metal-based and metal-free catalysts are used. Metal-free catalysts are less expensive than metal-based catalysts and do not have the disadvantages of oxidation and poisoning. Metal-free catalysts doped with heteroatoms, carbon materials, and polymers have been investigated for their high catalytic activity in hydrogen production. Carbon materials are typically high-surface-area carbon forms such as activated carbon, carbon nanotubes, fullerene, graphite, and graphene. In addition, heteroatoms are obtained by adding atoms to carbon materials, such as replacing carbon atoms with heteroatoms such as N, P, or B or bonding heteroatoms such as S, CI, Br, or O to the carbon surface. Hydrogen is produced from boron-based chemical hybrids, water, and other sources. Sodium borohydride (NaBH4), ammonium borane (NH3BH3), and hydrazine borane (N2H4BH3) are boron-based hybrid chemical sources. Examining the different production methods of these hydrogen sources is important for achieving cheaper and more efficient hydrogen production. Water splitting is examined in three categories: electrolysis, thermolysis, and photoelectrolysis. Furthermore, catalyst characterization is a technique that must be studied to relate catalytic activities with their properties. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, Fourier transform infrared spectroscopy, and thermogravimetric and differential thermal analysis techniques are examined to determine the composition and structure of metal-free catalyst surfaces. © 2022 Elsevier Inc. All rights reserved.