Carbon Nanomaterials for Energy and Biorelated Catalysis: Recent Advances and Looking Forward

Abstract

Along with the wide investigation activities in developing carbon-based, metal-free catalysts to replace precious metal (e.g., Pt) catalysts for various green energy devices, carbon nanomaterials have also shown great potential for biorelated applications. This article provides a focused, critical review on the recent advances in these emerging research areas. The structure-property relationship and mechanistic understanding of recently developed carbon-based, metal-free catalysts for chemical/biocatalytic reactions will be discussed along with the challenges and perspectives in this exciting field, providing a look forward for the rational design and fabrication of new carbon-based, metal-free catalysts with high activities, remarkable selectivity, and outstanding durability for various energy-related/biocatalytic processes.

Figure 1

Structure of carbon nanomaterials: diamond, graphite, C₆₀, CNTs, graphene, and 3D graphene-CNT hybrid materials. Images reprinted with permission from ref (34). Copyright 2012, Elsevier.

Figure 2

(a) Charge density distribution based on calculations for nitrogen-doped CNTs (N-CNTs). (b) Possible adsorption modes of an O₂ molecule on CNTs (top) and N-CNTs (bottom). (c) Atomic-resolution transmission electron microscopy (AR-TEM) image of the SeGnP edge. (d) IRR mimetic diagram on the SeGnP surface. (e) Schematic representation of charge transfer and of ORR process on PDDA-CNT. (f) Free-energy values for ORR of different kinds of defects. (g) AR-TEM image of DG. Hexagons: orange, pentagons: green, heptagons: blue, and octagons: red. Images reprinted with permission from refs (, , , , and 68). Copyright 2009 AAAS, 2016 AAAS, 2011 American Chemical Society, 2015 American Chemical Society, and 2016 Wiley–VCH.

Figure 3

(a, b) Schematic and scanning electron microscope (SEM) image of the 3D SWCNT-bridged graphene block on the cross-section. (c) Schematic for the synthesis and microstructures of a 3D graphene-RACNT fiber. (d) SEM image (top view) of the 3D graphene-RACNT fiber. (e, f) TEM images of graphene sheet connecting to the open tips of RACNTs under different magnifications. (g) SEM image of the wire-shaped DSSC from the cross-section view. Images reprinted with permission from refs ( and 36). Copyright 2015 American Chemical Society, 2015 AAAS.

Figure 4

(a) N 1s XPS spectra of HOPG model catalysts. (b) ORR activities for these model catalysts in (a). The inset: nitrogen contents of the catalyst models. (c) Schematic pathway for ORR on N-doped carbon nanomaterials. (d) Geometries of N atoms (sp-N, pyri-N, amino-N, and grap-N atoms) in graphdiyne. (e) N K-edge XANES of N doped graphdiyne (NFLGDY) prepared under temperatures of 700, 800, and 900 °C. A broaden and red-shifted peak ca. 397.4 eV appeared when the temperature increased, indicating the presence of the sp-N doping type. (f) ORR current densities @0.65 V for samples with different amounts of sp-N atoms. (g) Schemes of proposed active sites for the H₂O₂ generation on mild reduction of GO (F-mrGO) and F-mrGO(600) (F-mrGO annealed at 600 °C). Images reprinted with permission from refs (, , and 98). Copyright 2016 AAAS, 2018 Nature Publishing Group, and 2018 Nature Publishing Group.

Figure 5

(a) Schematic of bifunctional SiNC with catalytic activity for both CO₂RR and OER for the CO₂ overall splitting. (b) HAADF image of porous SiCN. (c) Current density, cathode, and electrode potentials of CO₂ overall splitting with two SiNC electrodes. (d) A generic mechanism for N₂RR to NH₃ on heterogeneous catalysts. (e) Schematic illustration of the preparation of NPCs. (f) Production rates of NH₃ and current efficiency of NPCs sample during 10 cycles at a given potential of −0.9 V. (g) The catalyst model with N-doped highly disordered carbon for N₂RR. (h) TEM image of the corresponding catalyst of (g). Images reprinted with permission from refs (, , , and 114). Copyright 2018 Wiley–VCH, 2016 Elsevier, 2018 American Chemical Society, and 2018 Elsevier.

Figure 6

(a) The redox potentials of various reactions with respect to the theoretical position of the g-C₃N₄ band edges at pH 7. (b) TEM image of the CDots-C₃N₄ composite. The inset: A magnified TEM image from region marked in red. (c) Band structure diagram for CDots-C₃N₄. VB, valence band; CB, conduction band. (d) H₂ and O₂ production from water splitting with CDots-C₃N₄ as photochemical catalyst. (e) AFM image of the mesoporous g-C₃N₄ nanomesh with monolayer structure. The inset: enlarged view of the rectangle area. (f) Height profiles along the lines in (e). (g) UV–vis diffuse reflectance spectra of OCN-tubes. (h) Schematic illustration of valence and conduction bands of H-terminated diamond, respectively. (i) Comparison of NH₃ yield from H-terminated and O-terminated diamond samples. Images reprinted with permission from refs (, , , , and 124). Copyright 2017 Elsevier, 2015 AAAS, 2016 American Chemistry Society, 2017 Wiley-VCH, and 2013 Nature Publishing Group.

Figure 7

(a) Schematic illustrations for the assembly of a MEA with the VA-NCNTs. C.E., R.E., W.E., stand for counter electrode, reference electrode, and working electrode, respectively. (b) SEM image of the VA-NCNTs. (c) Digital photo and SEM images of the MEA after a durability test. (d) Cross-section SEM image of the N-G-CNT/KB/Nafion catalyst layer. The purple arrows indicate the parallelly separated N-G-CNT sheets with interdispersed KB particles. (e, f) Schematic illustrations of O₂ diffusion through KB separated N-G-CNT sheets and the densely packed N-G-CNT sheets, respectively. Images reprinted with permission from ref (157). Copyright 2016, AAAS.

Figure 8

(a) SEM image of NPMC-1000. (b) Scheme of the structure of NPMC foam and its building block. (b, c) Linear sweep voltammetry (LSV) curves of NPMC-1000, NPMC-1100, the RuO₂, and the Pt/C on an RDE electrode in 0.1 M KOH medium. (d) ORR and (e) OER volcano plots for N-doped graphene, P-doped graphene, and N,P-doped graphene, respectively. (f) Schematic of a primary Zn-air battery. A carbon paper coated with NPMC was employed as the air cathode (enlarge part), a Zn foil was used as anode, and the separator a glass fiber membrane filled KOH solution. (g) Schematic of graphene with N, P, and F tridoping as a multifunctional C-MFC for simultaneous ORR, OER, and OER. (h) Polarization and power density curves of Zn-air batteries using N, P, and F tridoped graphene as ORR/OER catalyst in the air electrode. (i) O₂ and H₂ generation volumes with respected to the water-splitting time, the N, P, and F tridoped graphene was used as the HER/OER catalyst. (j) Schematic of the integrated green energy devices based on a superior multifunctional C-MFC (N,S-3DPG). Images reprinted with permission from refs (, , and 22). Copyright 2015 Nature Publishing Group, 2016 Wiley-VCH, and 2017 Elsevier.

Figure 9

(a) Schematic drawing for the fabrication route of CDs@POSS. (b) TEM image of CD@POSS. Inset is the size distributions of the CDs. (c) Illustration of colorimetric detection of glucose by using glucose oxidase (GOx) and g-C₃N₄ peroxidase-like catalytic reactions. (d) Schematic of H₂O₂ reduction with TMB catalyzed by g-C₃N₄. Images reprinted with permission from refs ( and 177). Copyright 2016 Wiley-VCH and 2014 Elsevier.

Figure 10

(a) SEM image of N-HMCS, the inset is the corresponding TEM image. (b) Current–time response on N-HMCS electrode with successive injection of O₂^•– into 0.1 M deoxidized PBS with pH 7.4 at a given potential of −0.15 V. (c) LSV curves of the N,P-CMP-1000 catalyst in common PBS solution (top) and artificial tear (bottom), respectively. Inset: dissolved oxygen (DO) concentrations detected by a commercial DO sensor. In vitro cytotoxicity of N,P-CMP-1000 extracts against (d) human corneal epithelial cells determined by CCK-8 assay and (e) live/dead cell double staining assay. (f) Schematic of the potential using N,P-CMP-1000 for sensing DO in the wearable glasses to monitor eye health. Images reprinted with permission from refs ^and . Copyright 2018 Elsevier, 2018 Wiley-VCH.

Figure 11

(a) Processes of PTT and PDT using CNTs. (b) Schematic drawing of the sonosensitization process of PMCS for cancer therapy. (c) Synthetic procedures for GODFe₃O₄@DMSNs nanocatalysts. (d) The schematic diagram of the catalytic-therapeutic mechanism of GFD NCs for generating hydroxyl radicals toward cancer therapy. Images reprinted with permission from refs (−33). Copyright 2016 Dove Medical Press, 2018 Wiley-VCH, and 2017 Nature Publishing Group.