Photocatalytic and Photoelectrocatalytic Water Splitting by Porous g-C₃N₄ Nanosheets for Hydrogen Generation

Abstract

Semiconductor-based photocatalytic and photoelectrochemical water splitting is an ultimate source of hydrogen generation for tackling the ongoing fuel crisis. In this context, we have synthesized a highly porous N-rich g-C3N4 metal-free, nontoxic semiconductor through the polycondensation method. In the present work, we have discussed the major changes in the morphology of g-C3N4 after acidic exfoliation thoroughly by using transmission electron microscopy (TEM) and scanning electron microscopy (SEM) studies. The chemical purity of the as-synthesized materials was analyzed by using powder X-ray diffraction (PXRD). The specific surface area and porosity of the materials were obtained through Brunner–Emmet–Teller (BET) surface area studies. Besides this, the electronic structure of g-C3N4 was discussed through X-ray absorption near-edge spectroscopy (XANES), and the elemental composition was determined by using X-ray photoelectron spectroscopy (XPS). Moreover, the dependency of the sacrificial agents of g-C3N4 was discussed in detail by using sodium sulfide/sodium sulfite (Na2S/Na2SO3) and triethanolamine (TEOA). It was observed that exfoliated g-C3N4 shows remarkable hydrogen evolution in the presence of TEOA and an efficient quantum yield up to 12%, which is 1.7-fold higher than in the presence of Na2S/Na2SO3 (7%). Furthermore, to harness most of the solar light spectrum, a high current density and improved Faradaic efficiency during the photoelectrocatalysis have been reported.

Oxide based Heterostructured Photocatalysts for CO2 Reduction and Hydrogen Generation

“…[13] Till now, several pathways have been substantiated for CO 2 transformation into hydrocarbon based fuels such as photocatalysis, electrocatalysis and photoelectrocatalysis. [13][14][15] All these approaches demand effective catalytic systems that possess adequate amount of energy input for the activation of linear CO 2 which otherwise have thermodynamic stability owing to higher oxidized chemical state of carbon (Δ f G = À 394.3 kJ/mol). [16] Sequestering and converting CO 2 into environmentally benign byproducts is one of the most thrived research topics currently.…”

“…This has motivated researchers to convert and reutilize CO 2 in the renewable energy tasks as currently the energy demand of the world is not met with conventional fuels due to cost and supply barriers [13] . Till now, several pathways have been substantiated for CO 2 transformation into hydrocarbon based fuels such as photocatalysis, electrocatalysis and photoelectrocatalysis [13–15] . All these approaches demand effective catalytic systems that possess adequate amount of energy input for the activation of linear CO 2 which otherwise have thermodynamic stability owing to higher oxidized chemical state of carbon (Δ f G=−394.3 kJ/mol) [16] .…”

Graphene-Based Derivatives Heterostructured Catalytic Systems for Sustainable Hydrogen Energy via Overall Water Splitting

“…To accomplish cost-effectiveness and high reliability, more comprehensive, flexible energy systems and complex policy measures are required. In recent decades, hydrogen (H 2 ) extracted through green pathways has been appreciated as a remedy for resolving multiple environmental issues because it is the epitome of clean fuel [14][15][16]. When green H 2 energy is used as a fuel, it not only attributes as an excellent efficiency in energy transformation but also emerges as a zero-pollution producer as it yields water as a by-product, which does not require further treatment [17][18][19][20][21].…”

Type-II CuFe2O4/Graphitic Carbon Nitride Heterojunctions for High-Efficiency Photocatalytic and Electrocatalytic Hydrogen Generation

“…Designing semiconductor photocatalysts to power a new economic paradigm based on solar fuels as the primary energy currency has emerged as an urgent imperative in light of Paris climate goals to keep anthropogenic global warming below 1.5 °C. − In recent years, photocatalytic water splitting has attracted substantial attention. − Semiconductor heterostructures comprising disparate components are particularly attractive by dint of their ability to effectively separate charge carriers in analogy to photosynthetic pathways. − Graphitic-C 3 N 4 has attracted considerable attention as a “metal-free” photo/electrocatalyst and has a range of desirable properties such as being nontoxic and readily accessible from earth-abundant precursors. − However, the photocatalytic properties of g-C 3 N 4 are limited by a high electron–hole recombination rate. , A primary limitation of g-C 3 N 4 derives from its intrinsic electronic structure wherein the conduction band is primarily N 2p in origin, whereas the valence band is C 2p in origin; their substantial hybridization and resulting orbital overlap increases the recombination of electron–hole pairs. − To promote effective charge separation, band-engineered heterostructures with energetic offsets are required to promote interfacial charge transfer upon photoexcitation. − Such heterostructures with programmable charge transfer reactivity can effectively separate electrons and holes, thus enabling their utilization in photocatalytic reactions. − To enhance the photocatalytic activity of n-type g-C 3 N 4 , it is important to interface this material with a p-type semiconductor to establish thermodynamic band offsets that promote charge separation. In this work, we demonstrate heterostructures interfacing g-C 3 N 4 with p-type CuFe 2 O 4, which yields optimal energetic offsets resulting in charge separation. , Type-II heterostructures assembled based on the insertion of CuFe 2 O 4 nanoparticles between the galleries of g-C 3 N 4 show excellent electrocatalytic and photocatalytic performance in the presence of hole scavengers.…”