Enhanced Visible Photocatalytic Hydrogen Evolution of KN-Based Semiconducting Ferroelectrics via Band-Gap Engineering and High-Field Poling

Abstract

In various ferroelectric-based photovoltaic materials after low-band-gap engineering, the process by which high-field polarization induces the depolarizing electric field (E dp) to accelerate the electron–hole pair separation in the visible light photocatalytic process is still a great challenge. Herein, a series of semiconducting KN-based ferroelectric catalytic materials with narrow multi-band gaps and high-field polarization capabilities are obtained through the Ba, Ni, and Bi co-doping strategy. Stable E dp caused by high-field poling enhanced the visible photocatalytic hydrogen evolution in a 0.99KN–0.01BNB sample with a narrow band gap and optimal ferroelectricity, which can be 5.4 times higher than that of the unpoled sample. The enhanced photocatalytic hydrogen evolution rate can be attributed to the synergistic effect of the significant reduction of the band gap and the high-field-polarization-induced E dp. The change in the band position in the poled sample further reveals that high-field poling may accelerate the migration of carriers through band bending. Insights into the mechanism by which catalytic activity is enhanced through high-field-polarization-induced E dp may pave the way for further development of ferroelectric-based catalytic materials in the photocatalytic field.

[Fe2S2–Agx]-Hydrogenase Active-Site-Containing Coordination Polymers and Their Photocatalytic H2 Evolution Reaction Properties

“…The improved catalytic performance of polymer catalysts 2 and 3 might be ascribed to the structural stabilization of [FeFe] catalytic centers by forming [Fe 2 S 2 –Ag 2 ] clusters. It is well-known that the reduction band gap is helpful for meeting the requirements for H 2 production through water splitting. − 1 has a bigger E bg value than 2 and 3 , consistent with the photocatalytic H 2 generation experiments. The amount of H 2 produced from the heterogeneous catalysis of 2 and 3 is lower than that of the reported [Fe 2 S 2 ]-MOFs obtained by ligand exchange. , Therein, a three-component photochemical system, including photosensitizer, catalyst, and sacrificial reagent, is adopted.…”

Enhanced photovoltaic performance via polarization in Bi/Co co‐doped KN‐based ferroelectric ceramics

“…The Raman spectra of the doped samples show a significant reduction in peak intensity compared with pure KN, but the spectral characteristics of KN ceramic are still observed. The sharp mode (B 1 , B 2 )(TO2) at 192 cm −1 is associated with the long‐range ordering of the ferroelectricity in KN, and the weakening mode after doping indicates a break in the ferroelectric sequence 7 . The broadening and slight shift to lower wave numbers of the A 1 (TO) and A 1 (LO) vibrational modes is due to the partial replacement of Nb 5+ by Co 3+ /Co 2+ in the [BO6] octahedral configuration in KN, which also implies a tendency to shift from orthorhombic to the tetragonal phases.…”

“…Ferroelectric materials, which lack bulk inversion symmetry and have spontaneous polarizability, have many applications in fields such as piezoelectric transducers, 1,2 photovoltaic converters, 3,4 and photocatalysis. [5][6][7] Conventional photovoltaic devices imprisoned in the semiconductor energy band have a limited photogenerated voltage, 8 which is not sufficient for increasing the photovoltaic conversion efficiency. Ferroelectric photovoltaic materials with both bulk photovoltaic effect 9 and electrostatic potential at the nano-domain wall, 10 which can generate photovoltaic voltages above the bandgap, can further improve the photovoltaic conversion efficiency and are potential candidates for next-generation photovoltaic devices.…”

“…Recent studies have focused on energy harvesting and energy conversion. Ferroelectric materials, which lack bulk inversion symmetry and have spontaneous polarizability, have many applications in fields such as piezoelectric transducers, 1,2 photovoltaic converters, 3,4 and photocatalysis 5–7 . Conventional photovoltaic devices imprisoned in the semiconductor energy band have a limited photogenerated voltage, 8 which is not sufficient for increasing the photovoltaic conversion efficiency.…”

Extraordinary Promotion of Visible-Light Hydrogen Evolution for Graphitic Carbon Nitride by Introduction of Accumulated Electron Sites (BN2)

“…Hydrogen energy, as a sort of clean energy, has the obvious benefits of high energy density (120 MJ/kg), environmental friendliness, non-toxicity, and the combustion product innocuous to humans, which is expected to replace non-renewable fossil energy in the future. − The water was fully split as a source of hydrogen gas through a simple and low-energy approach, which has great potential for practical applications owing to the abundant water resources on earth and can further greatly alleviate the global energy crisis. − At present, the main industrial hydrogen production methods mainly include the water–gas reaction , and chloralkali process . However, the above-mentioned two methods are endowed with high energy consumption, precious expense, and harsh operating conditions, so they cannot be applied across every field. , Notably, clean and renewable solar energy can be effectively utilized by the green and cheap photocatalytic technology, indicating a potential application prospect in photocatalytic water splitting to produce H 2 gas. − The significant process of photocatalytic hydrogen evolution involves two main steps.…”