Electrocatalyst Formed from Activated Vacuum Residue and Method of Electrocatalytically Producing Hydrogen Peroxide

Aspects of the present disclosure are described in Maimuna U. Zarew, Mohamed Javid, and Almaz S. Jalilov; “Porous Carbon from Vacuum Residue as an Effective Electrocatalyst for a 2eOxygen Reduction Reaction in Alkaline Media”; Energy and Fuels, 2023, 37, 23, 19166-19175, which is incorporated herein by reference in its entirety.

The financial support of King Fahd University of Petroleum and Minerals (KFUPM), and the Deanship of Research Oversight and Coordination for funding this work through project DF191019 is gratefully acknowledged.

The present disclosure relates to an electrocatalyst that includes P-, N-, and S-doped porous carbon from activated petroleum vacuum residue, a method of forming the electrocatalyst, and a method of electrocatalytically producing hydrogen peroxide using the electrocatalyst.

The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present invention.

Many industries use hydrogen peroxide as a vital chemical in the production of medical disinfectants, paper bleaching, treatment of wastewater, and the synthesis of fine chemicals. This is because of its effective oxidation properties and eco-friendly nature. [Yamanaka, I., et. al., Angew. Chem., Int. Ed. 2003, 42, 3653-3655; Siahrostami, S., et. al., Nat. Mater. 2013, 12, 1137-1143; Lu, Z., et. al., Nat. Catal. 2018, 1, 156-162; and Fellinger, T. P., et. al., J. Am. Chem. Soc. 2012, 134, 4072-4075]. Even though hydrogen peroxide has wide application and significance, its major source is the industrial anthraquinone process which has a lengthy procedure, consumes high energy, and is not eco-friendly. [Campos-Martin, J. M., et. al., Angew. Chem., Int. Ed. 2006, 45, 6962-6984]. Due to the disadvantages of the industrial process, there is an urgent need to use more eco-friendly methods. The electrochemical process is a very good alternative, it is a very simple method using sustainable sources (water and Ofrom the air) to generate HOfrom a two-electron oxygen reduction reaction, but the process suffers problems of slow kinetics and is not very selective due to high competition with the four-electron mechanism. [Chang, Q., et. al., Nat. Commun. 2020, 11, 2178; Liu, Y., et. al., Angew. Chem., Int. Ed. 2015, 54, 6837-6841; Iglesias, D., et. al., Chem 2018, 4, 106-123; Pang, Y., et. al., ACS Catal. 2020, 10, 7434-7442; Liu, W., et. al., Appl. Catal., B 2022, 310, 121312; Wang, Y., et. al, Adv. Energy Mater. 2021, 11, 2003323; Sa, Y. J., et. al, Angew. Chem., Int. Ed. 2019, 58, 1100; Li, L., et. al., Adv. Energy Mater. 2020, 10, 2000789; and Zhang, C., et. al., ACS Sustainable Chem. Eng. 2021, 9, 9369-9375]. Therefore, there is a high need for very selective and active electrocatalysts. [Chang Z., et. al., J. Am. Chem. Soc. 2023, 145 (21), 11589-11598.]Researchers focus on the use of metal-free carbon-based electrocatalysts because they are very conductive, more economical, durable, and efficient ORR electrocatalysts for the synthesis of HO. For many years metal-doped-carbon electrocatalysts such as Pt, Hg, Au, Pd, etc. had been used but they are very scarce and non-economical even though they are selective to the two-electron pathway. [Verdaguer-Casadevall, A., et. al, Nano Lett. 2014, 14, 1603-1608; Slanac, D. A., et. al., J. Am. Chem. Soc. 2012, 134, 9812-9819; Jiang, Y., et. al., Adv. Energy Mater. 2018, 8,1801909; and Melchionna, M., Fornasiero, P., Chem 2019, 5, 1927-1928]. Several modifications have been made to the transition metal from a single atom to compounds such as CoSe, and FeOfor HOsynthesis, but they still show instability to corrosion. [Jung, E., et. al., Nat. Mater. 2020, 19, 436-442; Barros, W. R. P., et. al., Electrochim. Acta 2015, 162, 263-270; and Sheng, H., et. al., ACS Catal. 2019, 9, 8433-8442]. Therefore, there is a great need to design metal-free carbon-based material with good selectivity and stability. Doping using hetero atoms causes intrinsic defects that improve the electronic properties of carbon-based electrocatalysts thereby making it more selective and active. These heteroatoms (N, P, B, S, etc.) vary in their atomic radii and electronegativity, this variation of doping different hetero-atoms into carbon-based framework can cause the rearrangement of local electronic structure making it more catalytically active. [Xia, Y., et. al., Nat. Commun. 2021, 12, 4225; Melchionna, M., et. al., Adv. Mater. 2019, 31, 1802920; Jiao, Y., et. al., J. Am. Chem. Soc. 2014, 136, 4394-4403; Chen, G., et. al., Nano Res. 2019, 12, 2614-2622; and Zhang, J., et. al., Nano-Micro Lett. 2021, 13, 65].

Accordingly, it is an objective of the present disclosure to provide an electrocatalyst for hydrogen peroxide production that overcomes the limitations described above.

The present disclosure relates to an electrocatalyst, comprising a microporous network of carbon comprising phosphorus, sulfur, and nitrogen dopant atoms, wherein a portion of the phosphorous is present as isolated phosphorous atoms doped into the microporous network of carbon.

In some embodiments, the microporous network of carbon comprises 70.0 to 78 wt % carbon, 11 to 19 wt % oxygen; 3.50 to 8.0 wt % phosphorus, 2.0 to 5.0 wt % sulfur, and 0.25 to 1.5 wt % nitrogen based on a total weight of electrocatalyst by XPS.

In some embodiments, the microporous network of carbon has a BET surface area of 300 to 4000 m/g, a pore volume of 0.2 to 2.4 cm/g, and a micropore volume of 0.1 to 2.3 cm/g.

In some embodiments, a surface of the microporous network of carbon includes carboxylate functional groups and phosphate functional groups.

In some embodiments, the microporous network of carbon has a ratio of a D band intensity to a G band intensity I/Iof 0.75 to 1.25 by Raman spectroscopy.

The present disclosure also relates to a method of producing the electrocatalyst, the method comprising mixing petroleum vacuum residue and phosphoric acid to form a crude mixture, annealing the crude mixture at 375 to 525° C. in a first inert atmosphere for 1 to 5 hours to form an intermediate product, and heating the intermediate product at 400 to 900° C. in a second inert atmosphere for 1 to 5 hours to form the electrocatalyst.

In some embodiments, the petroleum vacuum residue and phosphoric acid are present in the crude mixture in a ratio of 1.5:1 to 1:1.5 by weight.

In some embodiments, the petroleum vacuum residue comprises 80.0 to 85 wt % carbon, 7 to 9 wt % hydrogen, 3.0 to 5.0 wt % sulfur, and 0.25 to 1.0 wt % nitrogen based on a total weight of petroleum vacuum residue.

In some embodiments, the phosphoric acid has a concentration of 50 to 99% in water.

In some embodiments, the first and second inert atmosphere are flowing nitrogen gas.

In some embodiments, the annealing and heating are performed with a temperature increase rate of 5 to 10° C./min.

In some embodiments, the method does not involve reduction with hydrogen gas.

In some embodiments, the method further comprises washing the electrocatalyst with water and drying at 25 to 100° C.

The present disclosure also relates to a method of producing hydrogen peroxide, the method comprising applying a potential between a counter and a working electrode in an electrochemical cell containing an electrolyte to form hydrogen peroxide and collecting the hydrogen peroxide, wherein the working electrode includes the electrocatalyst; and wherein the electrolyte including an aqueous solution of a base at a concentration of 0.001 to 5 M.

In some embodiments, the method has an onset potential of 0.750 to 0.875 V vs RHE.

In some embodiments, the working electrode has a Tafel slope of 80 to 115 mV/dec.

In some embodiments, the method has an electron transfer number of 1.75 to 3.

In some embodiments, the method has a yield of 80 to 95% OHat a potential of 0.5 to 0.65 V vs RHE.

In some embodiments, the aqueous solution of a base at a concentration of 0.001 to 5 M is 0.1 M KOH is saturated with oxygen.

In some embodiments, the working electrode further comprises glassy carbon and a sulfonated fluoropolymer, and the electrocatalyst is disposed on the surface of the glassy carbon.

In the following description, it is understood that other embodiments may be utilized and structural and operational changes may be made without departure from the scope of the present embodiments disclosed herein.

When describing the present disclosure, the terms used are to be construed in accordance with the following definitions, unless a context dictates otherwise.

Embodiments of the present invention will now be described more fully hereinafter with reference to the accompanying drawings wherever applicable, in that some, but not all embodiments of the disclosure are shown.

As used herein the words “a” and “an” and the like carry the meaning of “one or more.”

As used herein, the terms “optional” or “optionally” means that the subsequently described event(s) can or cannot occur or the subsequently described component(s) may or may not be present (e.g., 0 wt. %).

Furthermore, the terms “approximately”, “approximate”, “about”, and similar terms generally refer to ranges that include the identified value within a margin of 20%, 10%, or preferably 5%, and any values therebetween.

The use of the terms “include”, “includes”, “including,” “have,” “has,” or “having” should be generally understood as open-ended and non-limiting unless specifically stated otherwise.

As used herein, “nanoparticles” are particles having a particle size of 1 nm to 500 nm within the scope of the present invention.

As used herein, “particle size” and “pore size” may be thought of as the lengths or longest dimensions of a particle and of a pore opening, respectively. The term “mesopore” as used herein refers to a pore having a diameter of 40 to 100 Å. The term “micropore” refers to a pore having a diameter of less than 40 Å. The term “macropore” refers to a pore having a diameter that exceeds 100 Å.

As used herein, the term “room temperature” refers to a temperature range of “25° C.±3° C. in the present disclosure.

As used herein, the term “electrode” refers to an electrical conductor used to contact a non-metallic part of a circuit, such as a semiconductor, an electrolyte, a vacuum, or air.

As used herein, the term “current density” refers to the amount of electric current traveling per unit cross-section area.

As used herein, the term “Tafel slope” refers to the relationship between the overpotential and the logarithmic current density.

As used herein, the term “electrochemical cell” refers to a device capable of either generating electrical energy from chemical reactions or using electrical energy to cause chemical reactions.

As used herein, the term “overpotential” refers to the difference in potential that exists between a thermodynamically determined reduction potential of a half-reaction and the potential at which the redox event is experimentally observed. The term is directly associated with a cell's voltage efficacy. In an electrolytic cell, the occurrence of overpotential implies that the cell needs more energy as compared to that thermodynamically needed to drive a reaction. The quantity of overpotential is specific to each cell design and varies across cells and operational conditions, even for the same reaction. Overpotential is experimentally measured by determining the potential at which a given current density is reached.

The present disclosure is intended to include all hydration states of a given compound or formula, unless otherwise noted or when heating a material.

In addition, the present disclosure is intended to include all isotopes of atoms occurring in the present compounds and complexes. Isotopes include those atoms having the same atomic number but different mass numbers. By way of general example, and without limitation, isotopes of hydrogen include deuterium and tritium. Isotopes of naturally occurring carbon includeC,C, andC. Isotopes of oxygen includeO,O, andO. Isotopes of naturally occurring nitrogen areN andN. Isotopes of naturally occurring sulfur includeS,S,S, andS. Isotopes of naturally occurring phosphorous includeP andP. Isotopically-labeled compounds of the disclosure may generally be prepared by conventional techniques known to those skilled in the art or by processes analogous to those described herein, using an appropriate isotopically-labeled reagent in place of the non-labeled reagent otherwise employed.

In general, a microporous network can have any suitable structure or form. The microporous network has micropores, but may also have other types of pores in addition to the micropores. Such other types of pores may be mesopores and/or macropores. In some embodiments, the microporous network comprises open pores. A network that comprises open pores may be referred to as an “open cell network” or other similar term. Open pores are pores that have solid edges and open faces, and fluid flow is possible to penetrate among them. This type of pore is in contrast to closed pores which form a “closed cell network”. Closed pores are pores that are connected via solid faces with no interconnectivity among them. In some embodiments, the microporous network further comprises closed pores. Open pores may be advantageous for increasing a catalytically active surface area. Open pores may allow for flow of gases and/or liquids into the network such that the gases and/or liquids can contact interior surfaces of interior pores.

In general, the network of pores may be ordered or disordered. An ordered network of pores refers to a network having a regular or periodic arrangement of pores that repeats throughout the network. Ordered networks of pores typically have relatively uniform pore sizes. A disordered network of pores refers to a network lacking a regular or periodic arrangement of pores. In a disordered network of pores, pores may be randomly arranged. Disordered networks of pores may be regular pore sizes, irregular pore sizes, or regions of regular pore sizes and regions of irregular pore sizes. In some embodiments, the microporous network of pores is ordered. In some embodiments, the microporous network of pores is disordered.

According to a first aspect, the present disclosure relates to an electrocatalyst. The electrocatalyst includes a microporous network of carbon comprising phosphorus, sulfur, and nitrogen dopant atoms.

In some embodiments, the microporous network of carbon comprises 70 to 78 wt % carbon, preferably 70.5 to 77.5 wt %, preferably 71.0 to 77.0 wt %, preferably 71.5 to 76.5 wt % carbon, preferably 72.0 to 76.0 wt % carbon, preferably 72.25 to 75.5 wt % carbon, preferably 72.5 to 75.25 wt % carbon, preferably 72.75 to 75.0 wt % carbon, preferably 73.0 to 74.75 wt %, carbon preferably 73.25 to 74.5 wt % carbon, preferably 73.5 to 74.25 wt % carbon, preferably 73.75 to 74.0 wt % carbon, based on a total weight of the microporous network of carbon.

In some embodiments, the microporous network of carbon comprises 11 to 19 wt % oxygen, preferably 11.5 to 18.75 wt % oxygen preferably 12.0 to 18.5 wt % oxygen preferably 12.5 to 18.25 wt % oxygen preferably 13.0 to 18.0 wt % oxygen preferably 13.5 to 17.75 wt % oxygen preferably 14.0 to 17.5 wt % oxygen preferably 14.5 to 17.25 wt % oxygen, preferably 15.0 to 17.0 wt % oxygen, preferably 15.25 to 16.5 wt % oxygen, preferably 15.5 to 16.25 wt % oxygen, preferably 15.75 to 16.0 wt % oxygen, based on a total weight of the microporous network of carbon.

In some embodiments, the microporous network of carbon comprises 3.50 to 8.00 wt % phosphorus, preferably 3.75 to 7.50 wt % phosphorus, preferably 4.00 to 7.00 wt % phosphorus, preferably 4.25 to 6.75 wt % phosphorus, preferably 4.50 to 6.50 wt % phosphorus, preferably 4.75 to 6.75 wt % phosphorus, preferably 5.00 to 6.50 wt % phosphorus, preferably 5.25 to 6.25 wt % phosphorus, preferably 5.50 to 6.00 wt % phosphorus, preferably 5.60 to 5.85 wt % phosphorus, preferably 5.70 to 5.75 wt % phosphorus, based on a total weight of the microporous network of carbon.

In some embodiments, the microporous network of carbon comprises 2.00 to 5.00 wt % sulfur, preferably 2.75 to 4.75 wt % sulfur, preferably 2.50 to 4.50 wt % sulfur, preferably 2.75 to 4.25 wt % sulfur, preferably 3.00 to 4.00 wt % sulfur, preferably 3.25 to 3.85 wt % sulfur, preferably 3.40 to 3.75 wt % sulfur, preferably 3.50 to 3.60 wt % sulfur, based on a total weight of the microporous network of carbon.