Zhi-Jian Zhao

Synergism of Geometric Construction and Electronic Regulation: 3D Se‐(NiCo)Sx/(OH)x Nanosheets for Highly Efficient Overall Water Splitting

The exploration of highly efficient electrocatalysts for both oxygen and hydrogen generation via water splitting is receiving considerable attention in recent decades. Up till now, Pt-based catalysts still exhibit the best hydrogen evolution reaction (HER) performance and Ir/Ru-based oxides are identified as the benchmark for oxygen evolution reaction (OER). However, the high cost and rarity of these materials extremely hinder their large-scale applications. This paper describes the construction of the ultrathin defect-enriched 3D Se-(NiCo)Sx /(OH)x nanosheets for overall water splitting through a facile Se-induced hydrothermal treatment. Via Se-induced fabrication, highly efficient Se-(NiCo)Sx /(OH)x nanosheets are successfully fabricated through morphology optimization, defect engineering, and electronic structure tailoring. The as-prepared hybrids exhibit relatively low overpotentials of 155 and 103 mV at the current density of 10 mA cm-2 for OER and HER, respectively. Moreover, an overall water-splitting device delivers a current density of 10 mA cm-2 for ≈66 h without obvious degradation.

Morphological and Compositional Design of Pd–Cu Bimetallic Nanocatalysts with Controllable Product Selectivity toward CO2 Electroreduction

Electrochemical conversion of carbon dioxide (electrochemical reduction of carbon dioxide) to value-added products is a promising way to solve CO2 emission problems. This paper describes a facile one-pot approach to synthesize palladium-copper (Pd-Cu) bimetallic catalysts with different structures. Highly efficient performance and tunable product distributions are achieved due to a coordinative function of both enriched low-coordinated sites and composition effects. The concave rhombic dodecahedral Cu3 Pd (CRD-Cu3 Pd) decreases the onset potential for methane (CH4 ) by 200 mV and shows a sevenfold CH4 current density at -1.2 V (vs reversible hydrogen electrode) compared to Cu foil. The flower-like Pd3 Cu (FL-Pd3 Cu) exhibits high faradaic efficiency toward CO in a wide potential range from -0.7 to -1.3 V, and reaches a fourfold CO current density at -1.3 V compared to commercial Pd black. Tafel plots and density functional theory calculations suggest that both the introduction of high-index facets and alloying contribute to the enhanced CH4 current of CRD-Cu3 Pd, while the alloy effect is responsible for high CO selectivity of FL-Pd3 Cu.

The Functionality of Surface Hydroxy Groups on the Selectivity and Activity of Carbon Dioxide Reduction over Cuprous Oxide in Aqueous Solutions

Carbon dioxide (CO2 ) reduction in aqueous solutions is an attractive strategy for carbon capture and utilization. Cuprous oxide (Cu2 O) is a promising catalyst for CO2 reduction as it can convert CO2 into valuable hydrocarbons and suppress the side hydrogen evolution reaction (HER). However, the nature of the active sites in Cu2 O remains under debate because of the complex surface structure of Cu2 O under reducing conditions, leading to limited guidance in designing improved Cu2 O catalysts. This paper describes the functionality of surface-bonded hydroxy groups on partially reduced Cu2 O(111) for the CO2 reduction reaction (CO2 RR) by combined density functional theory (DFT) calculations and experimental studies. We find that the surface hydroxy groups play a crucial role in the CO2 RR and HER, and a moderate coverage of hydroxy groups is optimal for promotion of the CO2 RR and suppression of the HER simultaneously. Electronic structure analysis indicates that the charge transfer from hydroxy groups to coordination-unsaturated Cu (CuCUS ) sites stabilizes surface-adsorbed COOH*, which is a key intermediate during the CO2 RR. Moreover, the CO2 RR was evaluated over Cu2 O octahedral catalysts with {111} facets and different surface coverages of hydroxy groups, which demonstrates that Cu2 O octahedra with moderate coverage of hydroxy groups can indeed enhance the CO2 RR and suppress the HER.

Low‐Coordinated Edge Sites on Ultrathin Palladium Nanosheets Boost Carbon Dioxide Electroreduction Performance

Electrochemical conversion of carbon dioxide (CO2 ) to value-added products is a possible way to decrease the problems resulting from CO2 emission. Thanks to the eminent conductivity and proper adsorption to intermediates, Pd has become a promising candidate for CO2 electroreduction (CO2 ER). However, Pd-based nanocatalysts generally need a large overpotential. Herein we describe that ultrathin Pd nanosheets effectively reduce the onset potential for CO by exposing abundant atoms with comparatively low generalized coordination number. Hexagonal Pd nanosheets with 5 atomic thickness and 5.1 nm edge length reached CO faradaic efficiency of 94 % at -0.5 V, without any decay after a stability test of 8 h. It appears to be the most efficient among all of Pd-based catalysts toward CO2 ER. Uniform hexagonal morphology made it reasonable to build models and take DFT calculations. The enhanced activity originates from mainly edge sites on palladium nanosheets.

Subsurface catalysis-mediated selectivity of dehydrogenation reaction

Subsurface Fe, Co, and Ni can promote the Pt-catalyzed propane dehydrogenation while exposed adversely on the surface. Progress in heterogeneous catalysis is often hampered by the difficulties of constructing active architectures and understanding reaction mechanisms at the molecular level due to the structural complexity of practical catalysts, in particular for multicomponent catalysts. Although surface science experiments and theoretical simulations help understand the detailed reaction mechanisms over model systems, the direct study of the nature of nanoparticle catalysts remains a grand challenge. This paper describes a facile construction of well-defined Pt-skin catalysts modified by different 3d transition metal (3dTM) atoms in subsurface regions. However, on the catalyst containing both surface and subsurface 3dTMs, the selectivity of propane dehydrogenation decreases in the sequences of Pt ~ PtFe > PtCo > PtNi due to the easier C–C cracking on exposed Co and Ni sites. After the exposed 3dTMs were removed completely, the C3H6 selectivity was found to increase markedly in the row Pt < PtNi@Pt < PtCo@Pt < PtFe@Pt, which is in line with the calculated trend of d-band center shifting. The established relationship between reactivity and d-band center shifting illustrates the role of subsurface catalysis in dehydrogenation reaction.