Comparison of Hydrogen Specification in National Standards for China

. Hydrogen specifications for different scenarios are various. Based on national standards for China, a comparison of hydrogen specification standards is discussed in this paper, including specification standards for industrial hydrogen, pure hydrogen, high pure hydrogen, ultrapure hydrogen, hydrogen for electronic industry and hydrogen for PEM FCVs. Hydrogen purity for electronic industry is greater than that for industrial hydrogen, pure hydrogen and hydrogen for PEM FCVs. Specifications of general contaminants in hydrogen for electronic industry, including H 2 O, O 2 , N 2 , CO, CO 2 and total hydrocarbons, are stricter than that in hydrogen for PEM FCVs. Hydrogen purity for PEM FCVs is less than that for electronic industry and pure hydrogen. However, contaminants in hydrogen for PEM FCVs are strict. Contaminants in hydrogen for PEM FCVs should include not only H 2 O, O 2 , N 2 , CO, CO 2 , Ar and total hydrocarbons, but also helium, total sulfur compounds, formaldehyde, formic acid, ammonia, halogenated compounds and particulates.


Introduction
Hydrogen has garnered more and more interest in recent years for its near-zero emission and abundant source. As is summarized by hydrogen council, hydrogen can play major roles in enabling large-scale renewable energy integration and power generation, distributing energy across sectors and regions, acting as a buffer to increase energy system resilience, decarbonizing transportation, decarbonizing industrial energy use, decarbonizing building heat and power, and providing clean feedstock for industry. Across the seven roles, hydrogen could account for 18% -20 % of total energy consumption by 2050, reducing annual CO 2 emission by roughly 60 Gt compared to today's technologies [1] .
Hydrogen economy is developing rapidly in China. By the end of 2018, more than 25 cities have announced to support the deployment of hydrogen industry. The cumulative sales number of hydrogen fuel cell vehicles reached 3428. About 23 hydrogen fuelling stations are in operation. More than 40 hydrogen fuelling stations are in construction and planning [2,3] .
Hydrogen is a secondary energy, which can be produced by coal gasification, steam reforming of natural gas, industrial gas purification, water electrolysis [4] , etc. Hydrogen specifications for different scenarios are various. According to national standards for China, a comparison of hydrogen specification standards is discussed in this paper, including standards for industrial hydrogen, pure hydrogen, high pure hydrogen, ultrapure hydrogen, hydrogen for electronic industry and hydrogen for proton exchange membrane fuel cell vehicles (PEM FCVs). Organization of this paper is as follows: In session 2, national standards for hydrogen specification are listed.
In session 3, a comparison of hydrogen specification in national standards is discussed, including hydrogen purity, total non-hydrogen gases and contaminants. In session 4, main conclusions are summarized.

National standards for hydrogen specification
As is shown in Table 1, there are five national standards for hydrogen specification in China. GB/T 3634.1-2006 specify the specification and requirements of testing, packing, storage, transportation and safety of industrial hydrogen. It is developed for petroleum, food, fine chemicals, glass and artificial gems manufacturing, metal smelting, cutting and welding industries. GB/T 3634.2-2011 specify the specification and requirements of testing, packing, storage, transportation and safety of pure hydrogen, high pure hydrogen and ultrapure hydrogen. It is developed for electronic, petrochemical, metal smelting industries, and scientific research. GB/T 16942-2009 specify the the specification and requirements of testing, packing, storage, transportation and safety of gaseous hydrogen for electronic industries. It is used as reducing gas, carrier gas for epitaxy process and gas for plasma etch. GB/T 34537-2017 specify the specification and requirements of hydrogen and compressed natural gas (HCNG) blends for vehicles. In this standard, it is specified that hydrogen used for HCNG blending should comply with GB/T 3634.1. GB/T 34537-2017 will not be discussed in this paper. GB/T 37244-2018 is now the only hydrogen fuel specification for proton exchange membrane fuel cell vehicles. Hydrogen fuel purity, contaminants and testing methods for contaminants are specified in this standard.  Table 2 shows the specification of hydrogen purity for different scenarios. As is specified in GB/T 3634.1, industrial hydrogen is classified into three grades, excellent grade (hydrogen purity ≥ 99.95%), first grade (hydrogen purity ≥ 99.50%) and qualified grade (hydrogen purity ≥ 99.00%). According to GB/T 3634.2-2011, hydrogen is classified into three grades, including pure hydrogen (hydrogen purity ≥ 99.99%), high pure hydrogen (hydrogen purity ≥ 99.999%) and ultrapure hydrogen (hydrogen purity ≥ 99.9999%). As is specified in GB/T 16942-2009, hydrogen for electronic industry is marked as three grades, involving Grade Ⅰ (hydrogen purity ≥ 99.9999%), Grade Ⅱ (hydrogen purity ≥ 99.9997%) and Grade Ⅲ (hydrogen purity ≥ 99.9995%). Hydrogen fuel for PEM FCVs is specified in GB/T 37244-2018. Hydrogen purity should not be less than 99.97%, which is greater than that of industrial hydrogen but less than that of pure hydrogen and hydrogen for electronic industry. Hydrogen for electronic industry specify the strictest hydrogen purity.
For industrial hydrogen and pure hydrogen there is no specific limitation of non-hydrogen gases. For high pure hydrogen, ultrapure hydrogen and hydrogen fuel for PEM FCVs, content of total non-hydrogen gases should not exceed content of total gases except hydrogen. Content of non-hydrogen gases in hydrogen for electronic industry is less than others. As is specified in GB/T 16942-2009, content of non-hydrogen gases should be less than or equal to 1.0 μmol/mol, 2.8 μmol/mol and 4.5 μmol/mol separately for Grade Ⅰ, Grade Ⅱ and Grade Ⅲ hydrogen.   There should be no free water in first grade hydrogen. Free water content in qualified hydrogen should not be greater than 100 mL/40 L gas cylinder. If qualified hydrogen is transported by piping or other packing forms, water content can be determined by suppliers and demanders.

Contaminants
As is specified in GB/T 3634.2-2011, water content in pure, high pure and ultrapure hydrogen should separately be less than or equal to 10 μmol/mol, 3 μmol/mol and 0.5 μmol/mol.
As is specified in GB/T 16942-2009, water content in hydrogen for electronic industry should be less than 0.2 μmol/mol, 0.2 μmol/mol and 0.5 μmol/mol separately for Grade Ⅰ, Grade Ⅱ and Grade Ⅲ hydrogen. The limitation of water content in hydrogen for electronic industry is less than that in the other hydrogen.
Water content in hydrogen for PEM FCVs should be less than or equal to 5 μmol/mol according to GB/T 37244-2018.
(2) Oxygen (O2) According to GB/T 3634.1-2006, oxygen content in industrial hydrogen is specified to be less than or equal to 0.01%, 0.20% and 0.40% separately for excellent grade, first grade and qualified grade hydrogen.
Oxygen content in pure and high pure hydrogen is separately specified to be less than or equal to 5 μmol/mol and 1 μmol/mol. For ultrapure hydrogen, total contents of oxygen and argon should be less than or equal to 0.2 μmol/mol.
As is specified in GB/T 16942-2009, oxygen content should be less than 0.2 μmol/mol for Grade Ⅰ and Grade Ⅱ hydrogen. While oxygen content should be less than 0.5 μmol/mol for Grade Ⅲ hydrogen. Oxygen content in hydrogen for PEM FCVs should be less than or equal to 5 μmol/mol, the same as that of pure hydrogen.

(3) Nitrogen (N2), Argon (Ar) and Helium (He)
Nitrogen, argon and helium are inert constituents. However, they dilute the hydrogen gas. For industrial hydrogen, total content of nitrogen and argon should separately be less than or equal to 0.04%, 0.30% and 0.60% for excellent grade, first grade and qualified grade hydrogen.
Nitrogen content in pure hydrogen, high pure hydrogen and ultrapure hydrogen should separately be less than or equal to 60 μmol/mol, 5 μmol/mol and 0.4 μmol/mol. Argon content in pure and high pure hydrogen can be determined by suppliers and demanders. Total contents of argon and oxygen should be less than or equal to 0.2 μmol/mol for ultrapure hydrogen. Nitrogen content of hydrogen for electronic industry should be less than 0.5 μmol/mol, 2.0 μmol/mol and 2 μmol/mol separately for Grade Ⅰ, Grade Ⅱ and Grade Ⅲ hydrogen.
Total contents of nitrogen and argon in hydrogen for PEM FCVs should be less than or equal to 100 μmol/mol. There is no specification of helium for industrial, pure, high pure, ultrapure and electronic industry used hydrogen. Helium content in hydrogen for PEM FCVs should be less than or equal to 300 μmol/mol.

(4) Carbon monoxide (CO)
As is specified in GB/T 3634.2-2011, CO content in pure, high pure and ultrapure hydrogen should separately be less than or equal to 5 μmol/mol, 1 μmol/mo1 and 0.1 μmol/mol. According to GB/T 16942-2009, CO content in hydrogen for electronic industry should be less than 0.05 μmol/mol and 0.5 μmol/mol for Grade Ⅰ and Grade Ⅲ hydrogen. Total content of CO and CO 2 should be less than 0.2 μmol/mol for Grade Ⅱ hydrogen. As is specified in GB/T 37244-2018, content of CO in hydrogen for PEM FCVs should be less than or equal to 0.2 μmol/mol.
According to GB/T 16942-2009, CO 2 content in hydrogen for electronic industry should be less than 0.05 μmol/mol and 0.5 μmol/mol for Grade Ⅰ and Grade Ⅲ hydrogen. Total content of CO 2 and CO should be less than 0.2 μmol/mol for Grade Ⅱ hydrogen. As is specified in GB/T 37244-2018, content of CO 2 in hydrogen for PEM FCVs should be less than or equal to 2 μmol/mol.
According to GB/T 16942-2009, total hydrogen carbons (CH 4 basis) should be less than or equal to 0.05 μmol/mol, 0.2 μmol/mol and 0.5 μmol/mol separately for Grade Ⅰ, Grade Ⅱ and Grade Ⅲ hydrogen. As is specified in GB/T 37244-2018, content of total hydrocarbons (CH 4 basis) in hydrogen for PEM FCVs should be less than or equal to 2 μmol/mol. When total hydrocarbons is greater than 2 μmol/mol due only to the presence of methane, total content of methane, nitrogen and argon should not exceed 100 μmol/mol. Oxygenated organic species are included in total hydrocarbons. (7) Total sulfur compounds Total sulfur compounds in hydrogen are only specified in GB/T 37244-2018 for PEM FVCs, which are severe poisons that at even low content can cause irreversible degradation of fuel cell performance [5,6] . The specification of total sulfur compound (H 2 S basis) should not exceed 0.004 μmol/mol. Based on the hydrogen production process, sulfur compounds can come from hydrogen production by stream reforming of natural gas, coal gasification, industrial gas purification, etc. H 2 S, COS, CS 2 and mercaptans should be involved. (8) Formaldehyde (HCHO) and Formic acid (HCOOH) HCHO and HCOOH in hydrogen are only specified in GB/T 37244-2018 for PEM FVCs, which similar to CO are severe poisons that adversely affects fuel cell performance [5] . Content of HCHO should be less than or equal to 0.01 μmol/mol. Content of HCOOH should be less than or equal to 0.2 μmol/mol. (9) Ammonia (NH3) NH 3 in hydrogen is only specified in GB/T 37244-2018 for PEM FVCs, which can cause some irreversible fuel cell performance degradation by affecting the ion exchange capacity of the ionomer of the proton exchange membrane and/or electrode [5] . Content of NH 3 should be less than or equal to 0.1 μmol/mol. (10) Total halogenated compounds Total halogenated compounds in hydrogen are only specified in GB/T 37244-2018 for PEM FVCs, which can cause irreversible degradation of fuel cell performance [5] . Content of total halogenated compounds (halogenate ion basis) should be less than or equal to 0.05 μmol/mol. Halogenated compounds can include hydrogen bromide (HBr), hydrogen chloride (HCl), chlorine (Cl 2 ), and organic halides (R-X).
Based on the hydrogen production process, halogenated compounds can come from hydrogen production by chlor-alkali production process, etc.

Conclusions
A comparison of national standards for hydrogen specification is discussed in this paper. Based on analysis and comparison, concluding remarks are as follows: (1) Hydrogen purity for electronic industry is greater than that for industrial hydrogen, pure hydrogen and hydrogen for PEM FCVs.
(2) Specifications of general contaminants in electronic hydrogen, including H 2 O, O 2 , N 2 , CO, CO 2 and total hydrocarbons, are stricter than that in hydrogen for PEM FCVs.
(3) Hydrogen purity for PEM FCVs is less than that for electronic industry and pure hydrogen. However, contaminants in hydrogen for PEM FCVs are strict.
(4) Contaminants in hydrogen for PEM FCVs should include not only H 2 O, O 2 , N 2 , CO, CO 2 , Ar and total hydrocarbons, but also helium, total sulfur compounds, formaldehyde, formic acid, ammonia, halogenated compounds and particulates.