Metal‐Free Artificial Photosynthesis of Carbon Monoxide Using N‐Doped ZnTe Nanorod Photocathode Decorated with N‐Doped Carbon Electrocatalyst Layer

Abstract

hindered by serious challenges, including the high overpotential (or low rate) for the reduction of CO 2 and the low selectivity of the reaction forming a broad spectrum of product mixtures. [4] Thus, highly efficient AP for a desired single product is very difficult and requires advanced materials for photoelectrodes and electrocatalysts. Recently, ZnTe has been developed as a promising photocathode material for CO 2 reduction because of its beneficial properties such as a visible-light-active low bandgap (2.3 eV) and a strong driving force for CO 2 reduction with the most negative conduction band edge position (−1.63 V RHE ) among known p-type semiconductors. [5,6] However, ZnTe has drawbacks of low charge separation efficiency both in the bulk and on the surface, photo electrochemical (PEC) instability in aqueous solutions, and poor selectivity for CO 2 -derived products relative to water-derived hydrogen. [5][6][7][8] In the present study, we attempt to fabricate a highly effective ZnTe photocathode having a 1D nanorod structure with substitutional nitrogen doping into the Te sites in order to improve light harvesting and charge transport characteristics. Unlike the conventional N-doping method involving post-treatment using a N 2 , N 2 O, or NH 3 gas, sodium amide (NaNH 2 ) precursor is utilized in the electrode preparation step to achieve nontoxic, one-step N-doping at a low temperature. [9][10][11][12] In addition, a N-doped carbon (N:C) overlayer is employed as the electrocatalyst instead of typical precious metals such as Au, Re, Pt, and Rh. Thus, charge transfer is facilitated because of the unique high conductivity of carbon and CO is selectively produced by stabilization and activation of the surface-bound CO 2 on the N sites with lone-pair electrons. [13][14][15] Here, we strategically fabricate the N-doped carbon electrocatalyst by annealing a polymer obtained from hexamethylenetetramine (HMT) and resorcinol. [16] The combination of the N-doped ZnTe nanorod photocatalyst and the N-doped carbon electrocatalyst layer affords an efficient photocathode for the photoelectrochemical reduction of CO 2 to fuels under sunlight at a low applied bias. At −0.11 V RHE (the theoretical CO 2 /CO redox potential), the integrated photocathode exhibits photocurrents at least fourfold higher than that observed with bare ZnTe nanorods. In addition, the An artificial photosynthesis system based on N-doped ZnTe nanorods decorated with an N-doped carbon electrocatalyst layer is fabricated via an all-solution process for the selective conversion of CO 2 to CO. Substitutional N-doping into the ZnTe lattice decreases the bandgap slightly and improves the charge transfer characteristics, leading to enhanced photoelectrochemical activity. Remarkable N-doping effects are also demonstrated by the N-doped carbon layer that promotes selective CO 2 -to-CO conversion instead of undesired water-to-H 2 reduction by providing active sites for CO 2 adsorption and activation, even in the absence of metallic redox centers. The photocathod...

RETRACTED ARTICLE: Colloidal silver diphosphide (AgP2) nanocrystals as low overpotential catalysts for CO2 reduction to tunable syngas

“…At the CO 2 -to-CO reduction potential of −0.11 V vs. RHE, n + p-Si/Al 2 O 3 /AgP 2 achieves a total current density ( j −0.11, total ) of −5.2 mA cm −2 . The remarkable j −0.11, total is higher than that of the other photocathodes towards CO 2 reduction, such as Au 3 Cu NP/Si NW ( j −0.11,total = −2.2 mA cm −2 ) 20 , RA-Au/n + p-Si ( j −0.11,total = −4.0 mA cm −2 ) 21 , N:C/N:ZnTe ( j −0.11,total = −1.2 mA cm −2 ) 54 , and Cu-ZnO/GaN/n + p-Si ( j −0.11,total = −1.2 mA cm −2 ) 55 . The Faradaic efficiency for H 2 and CO in the potential range from −0.6 to 0.2 V vs. RHE is summarized in Fig.…”

Rational design of photocatalysts for ammonia production from water and nitrogen gas

“…Heteroatom doping Heteroatom doping involves intentional introduction of impurity atoms into the lattices of materials to change their optical and electrical properties [42][43][44]. Depending on the species and degree (concentration) of dopants, changes, in the bandgap energy, band alignment, charge separation efficiency, and N 2 adsorption ability are expected.…”

Electrochemically anodized one-dimensional semiconductors: a fruitful platform for solar energy conversion

“…Among which, PEC CO 2 reduction technique has been regarded as an efficient and promising route to harness solar energy since it is economically feasible and environmentally benign. Among diverse semiconductors, spatially ordered 1D nanostructures are especially suitable for PEC CO 2 reduction on account of their unique structural merits [148,[150][151][152]. For instance, Song and co-workers fabricated Si photoelectrode with nanoporous Au mesh as co-catalyst by electrochemical anodization for highly selective and efficient PEC CO 2 reduction under simulated solar light irradiation [146].…”