Herein, Fe doped CoP nanoparticles (Fe-CoP NPs) encapsulated in porous N-doped carbon (PNC)/carbon nanotubes (CNTs) have been successfully synthesized. The Fe doping and confined structures resulted in enhanced charge transfer...

As the core of an electrocatalyst, the active site is critical to determine its catalytic performance in the hydrogen evolution reaction (HER). In this work, porous N-doped carbon-encapsulated CoP nanoparticles on both sides of graphene (CoP@ NC/GR) are derived from a bimetallic metal−organic framework (MOF)@graphene oxide composite. Through active site engineering by tailoring the environment around CoP and engineering the structure, the HER activity of CoP@NC/GR heterostructures is significantly enhanced. Both X-ray photoelectron spectroscopy (XPS) results and density functional theory (DFT) calculations manifest that the electronic structure of CoP can be modulated by the carbon matrix of NC/GR, resulting in electron redistribution and a reduction in the adsorption energy of hydrogen (ΔG H* ) from −0.53 to 0.04 eV. By engineering the sandwich-like structure, active sites in CoP@NC/GR are further increased by optimizing the Zn/Co ratio in the bimetallic MOF. Benefiting from this active site engineering, the CoP@NC/GR electrocatalyst exhibits small overpotentials of 105 mV in 0.5 M H 2 SO 4 (or 125 mV in 1 M KOH) to 10 mA cm −2 , accelerated HER kinetics with a low Tafel slope of 47.5 mV dec −1 , and remarkable structural and HER stability.

To design multi-heterointerfaces for doping-type electrocatalysts is a promising strategy to synergistically balance the catalytic activity/durability. In this study, we report a dual-MOFs/MXene composite derivation strategy to construct porous N-doped carbon encapsulating Fe-doped CoSe2 on both sides of MXene (Fe-CoSe2@PNC/TC). Combining multi-characterizations and density functional theory calculations, the Fe doping and well-designed multi-interfaces can induce the internal Se vacancy and electronic structure modulation, increasing and enhancing the active sites and, thus, reducing energy barriers for oxygen evolution reaction (OER). Thereby, the OER activities of Fe-CoSe2@PNC/TC powder materials have been significantly improved, which exhibits an overpotential of only 244 mV to attain 10 mA cm−2 with the long-term durability and a ultra-small Tafel slope of 41.1 mV dec−1 in 1.0 M KOH electrolyte (No IR correction), far outperforming the benchmark of commercial IrO2. This work proposes a controllable route combining multi-interface design and heteroatom doping for ultra-efficient OER electrocatalysis.

The rational construction of semiconductor nanoheterostructures is a feasible strategy to modulate electronic structure and increase active area of the electrocatalysts for biosensing. Herein, we develop an in situ approach, electrochemical (EC−) rebuilding of the smooth Cu surface, to construct hierarchical Co(OH) 2 nanosheets/CuO microcoral arrays (Co-(OH) 2 NSs/CuO MCAs). Through engineering the heterostructures by optimizing EC-rebuilding time, the electrocatalytic activity is significantly enhanced with a higher current density of glucose oxidation. The incorporation of Co(OH) 2 NSs into CuO MCAs also leads to a large active surface area and benefits surface/ interface reactions and mass transport for shorter response for glucose oxidation, higher current density, and better selectivity for glucose sensing. Both photoelectron spectra and density functional theory (DFT) calculations prove that interface charge transfers from CuO to Co(OH) 2 , resulting in electron redistribution and a significant increase in the adsorption energy of glucose. Compared with recently reported enzyme-free glucose sensors, the fabricated Co(OH) 2 NSs/CuO MCAs electrode exhibits excellent performance for enzyme-free glucose-sensing in alkaline electrolytes with a short response time (3 s), wide linear range of 500 nM to 2.311 mM, ultrasensitivity of 2269 mA mM −1 cm −2 , low limit of detection (LOD, 378 nM), and favorable reproducibility and stability. Noticeably, the outstanding response time, favorable ultrasensitivity, and great LOD are achieved in the glucose sensing. Therefore, the proposed sensor can be used for accurate quantification of glucose concentration in human serum with good repeatability, which will provide a new platform based low-cost semiconductor nano-heterostructures for rapid diagnostic tests and health monitoring.