Adv. Energy Mater. Overview: Graphyne—New Electrocatalyst New Carrier for Energy Conversion

[Background introduction]

As we all know, since the industrial revolution, the vigorous development of fossil fuels to promote economic development has led to the consumption of conventional fossil fuels in large quantities and triggered an energy crisis. In addition, the burning of fossil fuels has brought serious environmental problems such as greenhouse effect and particulate pollution. Therefore, there is an urgent need to develop economical, high-performance and environmentally-friendly technologies for energy conversion to solve the problems they face. Among them, electrocatalysis has great potential in energy conversion, but has high requirements for the performance of electrocatalysts. Therefore, it has become a basic challenge to develop a rich, high-performance and highly stable electrocatalyst. In recent years, electrocatalysts based on noble metals and layered double hydroxides have problems such as poor electrical conductivity, low active sites, and slow charge transfer. At present, carbon (C) materials such as graphene and carbon nanofibers have been widely used as carriers of various electrocatalysts to enhance their catalytic performance, and have been significantly improved. Wherein, since the graphite alkyne (GDY) SP coexist ^- and SP ^2- hybridized carbon atom, it has a high degree of π-conjugated electron ordered pore structure and adjustable regular structures, such GDY having a band gap and a natural High-speed carrier mobility. At ambient temperature, the electron and hole mobility in GDY can reach 105 cm ² V ^-1 s ^-1 . In addition, the mechanical properties of GDY can be changed by regulating different numbers of alkyne bonds and various stacking methods.

[Achievement Profile]

Recently, Dr. Li Bisheng (first author), Professor Zeng Guangming and Associate Professor Lai Cui (co-corresponding author) from the School of Environmental Science and Engineering of Hunan University reviewed the GDY-supported electrocatalysts, and reviewed the molecular structure, electronic properties, mechanical From the perspective of performance and stability, the reason why GDY can be used as a new carrier is analyzed. Next, various electrochemical applications of GDY-supported electrocatalysts in energy conversion are summarized, including hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), water decomposition (OWS), and nitrogen reduction reaction. (NRR). It also outlines the challenges that GDY and GDY-based materials face in future research. This article through the in-depth analysis of GDY to promote the development and application of this new carbon material. The research results were published in the internationally renowned journal Adv. Energy Mater. Under the title "Graphdiyne: A Rising Star of Electrocatalyst Support for Energy Conversion" .

[Graphic interpretation]

Figure 1. Molecular structure

(a) Schematic diagram of an aromatic group linking graphene with GY- via linear acetylene;

(Be) GYs with different numbers of alkyne bonds;

(Fg) From the top view, the optimized configurations of the two-layer GDY system are AB (β1) and AB (β2), respectively;

(Hj) From the top view, there are three possible configurations of the three-layer GDY system: ABA (γ1), ABC (γ2), and ABC (γ3) configurations.

Figure 2.

TEM and HRTEM images of NiO-GDY NC with GDY as the carrier (ad) of metal oxides .

(E) EDX mapping of Ni, O and C in NiO-GDY NC nanocube;

(F) Compare the high-resolution Ni 2p XPS spectra of NiO-GDY NC and original NiO NC;

(G) Charge density reference diagram of NiOGDY NC.

Figure 3. GDY as the transition metal chalcogenide carrier

(ab) eGDY / MoS ₂ , MoS ₂ and eGDY state density (DOS), where the Fermi level is 0 eV;

(Cd) Charge density difference chart of eGDY / MoS ₂ : top view and side view;

(E) Hydrogen adsorption free energy (ΔGH) on eGDY / MoS ₂ , eGDY and MoS ₂ ;

(F) Nyquist diagram of the catalyst in 0.5 MH ₂ SO ₄ ;

(G) Graph the scan rates of eGDY / MoS ₂ , CC / MoS ₂ , GDY and CC in the capacitor current of 0.70 V and RHE ;

(H) the instant photocurrent response of the catalyst;

(I) The eGDY / MoS ₂ polarization curve obtained before and after 3000 potential cycles ;

(J) An electrolytic cell using eGDY / MoS ₂ as a cathode under operating conditions .

Figure 4.

Schematic diagram of a novel three-layer sandwich nanostructure with hydrogen instead of GDY (HsGDY) as an intermediate layer; (a) Preparation of a three-layer nanotube array;

(B) HER polarization curve with iR compensation;

(C) Tafer diagram;

(D) The Nyquist diagram obtained from the EIS, whose equivalent circuits are R _s and R _ct ;

(E) In 0.5 MH ₂ SO ₄ , the current density changes of NiCoS-HsGDY-Ni, Co-MoS ₂ , NiCoMoS, NiCoS-HsGDY, NiCoS, HsGDY, Pt flakes and carbon paper with time, without iR compensation.

Figure 5. Theoretical calculation and structural analysis of electrocatalyst

(ac) Stable configuration of GDY, ICLDH and ICLDH-GDY;

(D) The charge density difference of the stable configuration ICLDH-GDY;

(Ef) XPS spectra of Fe 2p and Co 2p nuclear energy levels of e-ICLDH-GDY / NF structure;

(G) Raman spectra of GDY, ICLDH and e-ICLDH-GDY;

(H) Formation of free energy changes of OOH * and corresponding stable structures of GDY (ΔG1) and e-ICLDH-GDY (ΔG2);

(I) PDOS in 3d and 2p bands including the interface system of the GDY and ICLDH layers;

(J) PDOS of Fe 3d, Co 3d, H ₂ O-s and H ₂ O-p bands near the interface region ;

(K) Energy pathway of HER to e-ICLDH-GDY, ICDDH and GDY under alkaline conditions;

(L) Compare the transition state barriers for water decomposition in the three systems;

(M) H-chemical adsorption of these three systems.

Figure 6.

SEM, TEM, and HRTEM images of GDY as the carrier (ad) of the monoatomic catalyst ;

(Eh) SEM, TEM and HRTEM images of Pd ⁰ / GDY;

( Il) HAADF images obtained from various regions of the Pd ⁰ / GDY nanosheets;

( Mp) STEM-HAADF image of Pd ⁰ / GDY nanosheets and corresponding element mapping of Pd and C atoms.

Figure 7. Hydrogen evolution reaction (HER)

(a) Top view of optimized structure of GDY-MoS ₂ ;

(B) Free energy diagrams of HER at different positions in the original MoS ₂ , GDY, and GDY-MoS ₂ at equilibrium potentials based on DFT calculations ;

(C) DOS of the original MoS ₂ and GDY-MoS ₂ heterostructures;

(D) PDOS for GDY-MoS ₂ ;

(E) Linear sweep voltammetry (LSV) curve;

(F) the corresponding Tafel diagram of the synthesized electrocatalyst;

(G) LSV curves of GDY-MoS ₂ NS / CF and MoS ₂ NS / CF recorded before and after the continuous cycle test ;

(H) Overpotential at 10, 50, 100 and 200 mA cm ^-2 after every 1,000 cycles ;

(I) LSV curve in 0.5 MH ₂ SO ₄ .

Figure 8. Oxygen reduction reaction (ORR)

(a) Top view of the atomic configuration of * OOH, * O and * OH adsorbed on the surface of Fe-GDY;

(Bc) The free energy diagrams of the ORR 4e-path of the equilibrium electrode potential U4e ⁰and the experimentally measured starting potential U _onset on the surfaces of Fe-GDY and Pt (111) catalysts were calculated ;

(D) Cyclic voltammetry (CV) response of Fe-GDY catalyst and commercially available Pt / C catalyst in 0.1 M KOH solution saturated with N ₂ and O ₂ at room temperature ;

(E) Rotatable electrode measurement of Fe-GDY catalyst and commercially available 20 wt% Pt / C catalyst in O ₂ saturated 0.1 M KOH solution;

(F) Stability of Fe-GDY ORR catalyst.

Figure 9.

Chemical adsorption model of free energy calculated by completely decomposing water (ab) HER and OER;

(C) Calculate the free energy diagram of H ₂ O activation and H adsorption under alkaline conditions ;

(D) Free energy diagram of OER in alkaline medium;

(Ef) polarization curve;

(Gh) Corresponding Tafel diagrams of HER and OER in 1.0 M KOH;

(I) Polarization curves of CoN _x -GDY NS / NF before and after 10,000 cycles;

(J) Polarization curves of CoN _x -GDY NS / NF before and after 2000 cycles;

(K) CV curve of a synthetic sample in a two-electrode system;

(L) Current density curve of FeCH-GDY / NF with time at 10 mA cm ^-2 in alkaline electrolytic cell .

Figure 10. Electrochemical NRR performance of Mo ⁰ / GDY electrocatalyst

(a) UV-visible absorption spectrum after 2 h electrochemical NRR in 0.1 M Na ₂ SO ₄ electrolyte at different potentials;

(Bc) FEs and Y _NH3 in 0.1 M Na ₂ SO ₄ at different applied potentials ;

(D) Y _NH3 and FEs of NH ₃ produced by different batches of Mo ⁰ / GDY electrocatalyst ;

(E) Ultraviolet and visible absorption spectrum of Mo ⁰ / GDY electrocatalyst tested under N ₂ saturated and Ar saturated electrolytes ;

(F) the amount of NH ₃ produced by pure GDY and Mo ⁰ / GDY electrocatalysts after 2 h electrolysis at -1.2 V under ambient conditions ;

(Gh) FEs and Y _{NH3 at} different applied potentials in 0.1 M HCl ;

(I) The amount of NH ₃ produced by pure GDY and Mo ⁰ / GDY electrocatalysts after 2 h electrolysis at -0.1 V under ambient conditions .

[Summary and Prospect]

This article summarizes the structure and properties of GDY, including molecular structure, electronic properties, mechanical properties and stability. Based on these properties, the feasibility of GDY as an electrocatalyst carrier was also discussed. Then, various GDY-supported electrocatalysts were studied, and the role of GDY in these composites was emphasized. Specifically, the presence of GDY can improve carrier transfer efficiency, improve dispersibility, increase electrical conductivity, and accelerate mass transfer effects. Finally, the electrochemical applications of GDY supported electrocatalysts in energy conversion are reviewed. The results show that GDY supported electrocatalysts have high performance for various electrochemical applications such as HER, OER, ORR, OWS, and NRR.

Although GDY-based electrocatalysts have made some achievements in energy conversion, research in this field is still in its infancy, and there are still the following challenges and opportunities: (1) The development of large-scale, high-performance, and reasonably priced synthetic compounds is urgently needed. GDY and GYs technology, so as to provide a solid foundation for theoretical research and practical applications; (2) in addition to GDY, other methods of preparing GYs with different acetylene bonds such as GY, GY-3 and GY-4 are still in the theoretical stage, It is therefore worthwhile to obtain GY, GY-3 and GY-4 with adjustable structures and properties from the laboratory; (3) More recent characterization techniques should be adopted to fully understand the structure, properties and properties from the molecular level or even the atomic level. (4) Other modifications should be explored to make GDY reach the required band gap, electronic properties, mechanical properties and optical properties; (5) The application scope of GDY should not be limited to energy conversion. Because GDY also shows great potential in other applications such as sensors, drug carriers, gas separation, batteries, supercapacitors, and desalination, but research in these areas is still in its infancy, and more effort is needed to develop GDY Base material for practical applications. In short, I believe that all challenges and disadvantages can be overcome, and GDY-based materials will definitely be applied to various fields

Literature link: Graphdiyne: A Rising Star of Electrocatalyst Support for Energy Conversion (Adv. Energy Mater., 2020 , DOI: 10.1002 / aenm.202000177)

Source of information: material cattle