The present invention relates to the field of catalyst modified electrode for electrolysis. More particularly, present invention relates to metal nitride based nanocatalyst with protective conductive CN-coating modified bi-functional electrodes. Present invention also relates to catalysts for sustainable electrolysis of direct sea/low grade/ground water.
BACKGROUND OF THE INVENTION:
Electrolysis of water is the process of using electricity to decompose water into oxygen and hydrogen gas. Splitting water into hydrogen and oxygen presents an alternative to fossil fuels, but purified water is a precious resource. More than 80% of the world's population are exposed to high risk levels of water security. Freshwater is likely to become a scarce resource for many communities.
At the same time, low-grade water and saline water is a largely abundant resource. The requirement of high purity water for electrolysis and the widespread availability of seawater have led to significant research efforts in developing direct seawater electrolysis technology.
Electrolysis of mostly abundant sea water rather than scarce fresh water is not only a promising way to generate clean hydrogen energy, which also alleviates the use of highly demanding fresh water. Seawater electrolysis represents a potential solution to grid-scale production of hydrogen energy without reliance on freshwater.
Some reports have used photo-electrolysis as the mean and corresponding catalysts systems to achieve sustainable hydrogen production from brine water. These literatures though report similar targets, but the achievable margins are different in each case.

The Publication Kuang et. al., "Solar-driven, highly sustained splitting of seawater into hydrogen and oxygen fuels", PNAS April 2, 2019, 116 (14) 6624-6629 (https://doi.org/10.1073/pnas.1900556116) discloses a Ni-sulfide based catalyst system utilized for photo electrolysis of sea water.
The Publication Luo Yu et. al., "Hydrogen Generation from Seawater Electrolysis
over a Sandwich-like NiCoN|NixP|NiCoN Microsheet Array Catalyst", ACS
Energy Lett. 2020, 5, 8, 2681-2689
(https://doi.org/10.1021/acsenergylett.0c01244) discloses NiCON and NixP based sandwiched array utilized for sea water electrolysis that produced 10 mA/cm"2 current density at 165 mV.
The Publication Soren Dresp et.al., "Direct Electrolytic Splitting of Seawater: Opportunities and Challenges", ACS Energy Lett. 2019, 4, 4, 933-942 (https://doi.org/10.1021/acsenergylett.9b00220) discloses a review that enlightens the issues associated with electrolysis of sea water.
The Publication Wenming Tong et. al., "Electrolysis of low-grade and saline surface water", Nature Energy, Volume 5, pages 367-377 (2020) (https://doi.org/10.1038/s41560-021-00851-4) discusses the type of catalyst systems those may be useful for directly electrolyzing sea water with reference to low cost metals and the non-metal doping such as nitride, sulphide and phosphide.
The reported catalysts so far have not been successful to directly electrolyze sea water for a long duration. The existing catalysts are also known to generate low current density in sea water electrolyte.
The companies especially working towards commercialization of electrolysers and production of H2 are i.e. for example various oil & gas domain public sector and private sector companies.

Though, electrolysis is an established procedure, and a number of catalysts systems are available in literature exhibiting a broad range of efficiency, the electrolysis of sea water or low-grade water possessing various salts and ions are still under explored. The reason being the concurrent chlorine evolution reactions and catalyst degradation or deactivation. For example, presence of Mg salt in the electrolyte is known to get deposited on the electrode surface during electrolysis and ceases the activity of catalyst. Similarly, the chloride ions are known to migrate towards the anode surface during electrolysis and corrode the surface and notably decrease the lifetime of catalyst. Therefore, current commercial units use a preliminary unit to separate the salts before allowing the electrolyte to enter into the electrolysis chamber, which adds to the cost of electrolysis and hydrogen produced.
Most of the known electrocatalysts are unable to sustainably carry out electrolysis of sea water since CER (chlorine evolution reaction) interferes with the OER (oxygen evolution reaction) and the hydroxide deposition deactivates the catalyst.
Inventors of the present invention have developed a selective nanocatalyst system that is able to catalyse OER and not CER up to a reasonably high potential. The present inventors have also used a protective coating that prevents the migration of chloride ion towards the surface and prolonged the catalyst life. Overall, the electrode is capable of sustainably carrying out electrolysis of sea water at high current density for a very long period.
Therefore, problem(s) being solved by the present invention is that it provides direct sustainable electrolysis of sea water at high current density.
The present invention discloses a novel catalyst design having low cost, is sustainable and easily synthesized.

OBJECTS OF THE INVENTION:
The principal object of present invention is to provide a modified bi-functional electrode comprising metal nitride based nanocatalyst with protective conductive CN-coating for electrocatalysis.
Another object of the invention is to provide modification of electrodes with OER selective nanocatalyst followed by a conducting CN coating.
Another object of the invention is to provide a novel method of synthesis of a modified bi-functional electrode.
Another object of the invention is to provide a novel catalyst composition comprising said catalyst.
Another object of the invention is to provide a process for synthesis of nanocatalyst.
SUMMARY OF THE INVENTION:
In one aspect, the present invention discloses a modified bi-functional electrode comprising metal nitride based nanocatalyst with protective conductive CN-coating for electrocatalysis.
The said electrode comprises a selective nanocatalyst system that is able to catalyse OER and not CER up to a reasonably high potential.
The said electrode is active in the temperature range 0 to 80°C and all basic pH conditions.

In another aspect, the present invention discloses a novel synthetic process involving synthesis of the nanocatalyst and CN-coating of the electrode. The synthesis of catalyst followed by CN coating is carried out in-situ using a one-step procedure.
A method for preparation of modified bi-functional electrode, comprises the following steps:
a. coating of the electrode with active material;
b. synthesis of nanocatalyst;
c. coating of the catalyst and sacrificial agent on the activated commercial
electrode to form catalyst modified electrode; and
d. applying the CN coating on the above catalyst modified electrode,
wherein the steps of synthesis of nanocatalyst followed by CN coating is
sequential or simultaneous.
In the said method the synthesis of nanocatalyst followed by CN coating is carried out in-situ using a one-step procedure.
In the said method the sacrificial agent first acts as a reagent and subsequently leaves by allowing a conductive coating on the surface, and the conductive coating protects the electrode without strongly affecting the HER and OER.
The products of the said process are nanometallic nitrides/oxides/oxyhydroxides covered with a CN conductive coating.
In another aspect, present invention discloses a novel catalyst design having low cost, is sustainable and easily synthesized.
In another aspect present invention discloses a process for synthesis of nanocatalyst comprising:
i) Surface activation via hydrothermal procedure;

ii) Coating via solution cast procedure; and
iii) Heat treatment under controlled environment,
In the said process:
the hydrothermal treatment in the first step is carried out in the range of 30-80°C; the coating in the second step is carried out under room temperature and high-pressure conditions; and
the heating the precursor in the final step is carried out at 400°C for 3.5 h to synthesize the final catalyst.
In yet another aspect present invention discloses a mixed metal oxide-nitride N-doped carbon coated electrode system for catalytic application prepared with one step procedure to synthesise and coat the catalyst on the electrode surface and apply protective coating to the catalyst adsorbed on surface.
The aim of the present invention is to develop nanocatalyst and subsequent modified electrode systems that will be able to sustainably split sea water and low-grade water containing the poisonous cations and anions without losing catalytic activity.
BRIEF DESCRIPTION OF FIGURES:
Figure 1: Schematics of catalyst and electrode preparation.
Figure 2: The UV-Vis and DLS spectra of the metal nanoparticles used for electrode fabrication.
Figure 3: XPS spectra of the catalyst modified electrode showing the presence of metal nitride particles and N@C.
Figure 4: The OER plot and stability of modified electrode in pure water.

Figure 5: TEM images of Ni-Nx nanoparticle.
Figure 6: The HER (Hydrogen Evolution Reaction) and OER (Oxygen Evolution Reaction) stability in simulated sea water.
Figure 7: Effect of temperature on HER and OER of catalyst in sea water.
Figure 8: The effect of pH on the OER and HER of electrode in sea water.
Figure 9: The Tefel plot of the OER and HER activity of the catalyst
DETAILED DESCRIPTION OF THE INVENTION:
Present invention relates to catalysts for sustainable electrolysis of direct sea water, low-grade water, or ground water.
Present invention discloses a mixed metal oxide-nitride N-doped carbon coated electrode system for catalytic application.
The present invention discloses metal nitride based nanocatalyst with protective conductive CN-coating modified bi-functional electrodes for electrocatalysis.
The present invention is about product, i.e. a novel catalyst and subsequent electrode for electrocatalysis produced using the novel catalyst.
The modification of electrodes comprises OER selective nanocatalyst followed by a conducting CN coating for electrocatalysis.
Most of the known electrocatalysts are unable to sustainably carry out electrolysis of sea water since CER interferes with the OER and the hydroxide deposition deactivates the catalyst.

Present invention discloses a catalyst system that is selective towards OER compared to that of the CER and possibly the protective layer prevented the transport of CI- ion towards the electrode surface and overall, the product became viable for sustainable sea water electrolysis.
So far literature, the metal oxide nanoparticles were first synthesized, and these were subsequently utilized nano metal oxides via thermal treatment to synthesize the corresponding metal nitride nano-catalysts.
In the present invention, metal salts are being used to directly synthesize the metal nitride nanocatalyst using a polymeric nanoreactor approach. Moreover, the product is further converted to CN-based conductive coating in the same process.
The present invention is based on the catalyst synthesis and electrode fabrication part. Novelty of the present invention lies in the catalyst composition and the process utilized to achieve the same.
A new catalyst composition and a new one-step procedure to synthesise and coat the catalyst on electrode surface and apply protective coating to the catalyst adsorbed on surface has been disclosed.
A method for preparation of modified bi-functional electrode comprising nanocatalyst with protective conductive CN-coating comprises the following steps:
a. coating of the electrode with active material;
b. synthesis of nanocatalyst;
c. coating of the catalyst and sacrificial agent on the activated commercial
electrode to form catalyst modified electrode; and
d. applying the CN coating on the above catalyst modified electrode,
wherein, the steps of synthesis of nanocatalyst followed by CN coating is
sequential or simultaneous.

The present invention utilizes a two-step procedure for the same. The electrode is first coated with an active oxyhydroxide material. The catalyst precursor and the sacrificial agent is then coated on the activated electrode surface followed by CN-coating. The synthesis of catalyst followed by CN coating is carried out in-situ using a one-step procedure. Figure 1 discloses schematic representation of catalyst and electrode preparation.
The process of synthesis of nanocatalyst followed by CN coating become one-step and the control over the catalyst composition is tailored.
A conductive protecting layer used in this case, blocks the passage of bigger ions from reaching the electrode and improves the life of electrode.
A sacrificial agent used in the said method first acts as a reagent and subsequently leaves by allowing a conductive coating on the surface.
The products of the said process are typically nanometallic nitrides/oxides /oxyhydroxides covered with a CN conductive coating. Figure 3 discloses XPS spectra of the catalyst modified electrode showing the presence of metal nitride particles and N@C. These can be utilized for various electrocatalytic and other catalytic applications. Further modification of catalyst structure may lead to photocatalytic applications. Typically, the catalysts are suitable for electrolysis of H2O and may be utilized for CO2 conversion.
The starting materials possessing similar functionality can be varied to certain extent. For example, nitrogenous reagent such as N2 or NH3 or NH2NH2 etc can be utilized as the reagent for one of the synthetic steps. The polymeric agent may also be varied possessing similar functionality in the pendant group.
Present invention further discloses a mixed metal oxide-nitride N-doped carbon coated electrode system for catalytic application prepared with one step procedure

to synthesise and coat the catalyst on the electrode surface and apply protective coating to the catalyst adsorbed on surface.
Present invention discloses a process for synthesis of nanocatalyst comprises: i) Surface activation via hydrothermal procedure; ii) Coating via solution cast procedure; and iii) Heat treatment under controlled environment,
Though hydrothermal and heat treatment processes are utilized in literature to synthesize the catalyst, the role of the processes in present invention is different. This invention utilizes a one-step procedure to synthesize the nanocatalyst and coat the same with a CN conducting layer. Further, in this invention, the precursors used, and the catalyst obtained is new.
The reaction conditions in the present method are achievable with the use of readily available equipment such as furnace, stirrer, sonicator etc. The temperature pressure conditions need to be maintained as per the given protocol to produce materials with desired efficiency. The synthesis condition may be altered by minor degree depending upon the starting material used, though this is easily achievable by a person well versed with the Art.
Example of typical catalyst synthesis:
The hydrothermal treatment in the first step was carried out in the range of 30-80°C. The coating in the second step was carried out under room temperature and high-pressure conditions. In the final step the precursor was heated to 400°C for 3.5 h to synthesize the final catalyst.
Figure 2 discloses the UV-Vis and DLS spectra of the metal nanoparticles used for electrode fabrication.

Lab scale preparation of the electrode and evaluation of the efficiency towards sea water electrolysis is already validated.
The invention is modification of electrodes with OER selective nanocatalyst followed by a conducting CN coating. The catalyst is able to perform OER up to 2.5 V without affecting the chloride ion. The conductive coating is able to protect the electrode without strongly affecting the HER and OER. Figure 6 discloses the HER and OER stability in simulated sea water. Further Figure 9 shows the Tefel plot of the OER and HER activity of the catalyst.
The electrodes are active in the temperature range 0 to 80°C and all basic pH conditions. Figure 7 shows effect of temperature on HER and OER of catalyst in sea water and figure 8 shows the effect of pH on the OER and HER of electrode in sea water.
The developed catalyst and electrode selectively electrolyze water in presence of chloride and other ions for a long period -1000 h without losing activity.
The catalyst displays high current density in sea and low-grade water, which is an issue in conventional systems.
Overall, the catalyst modified electrode system is able to produce high purity H2 from sea water and low-grade water via electrolysis.
The catalyst modified electrode of the present invention prevented chlorine evolution reaction and catalyst degradation & deactivation during sea water electrolysis and elongated the catalyst life. This has rendered the possible commercialization of sea water electrolysis for H2 production
The catalyst modified electrode of the present invention can be of low cost, sustainable and can be easily synthesized.

The catalysts may be used for conversion of C02 to value added products.
The catalyst systems may be utilized for catalysing other chemical reactions.
The nanomaterials with suitable modification may be utilized for fuel cell applications.
The products of the present invention are suitable for direct electrolysis of water in presence of various salts and other impurities. The catalysts are able to generate high current density over a long period of time. These catalysts are bi-functional and suitable for both OER and HER applications. These can be synthesized in a large scale in an economical manner without using any sophisticated reaction set up.
The present inventors are assessing the large-scale implementation and possibly extending the fabrication techniques to different commercial electrode materials. Scope of the invention is to further optimize the catalyst size and composition and modify the conductive layer.
Presumably, this has substantial commercial application in electrolysers.

We claim:

1. A modified bi-functional electrode comprising the metal nitride based nanocatalyst coated with protective conductive CN-coating.
2. The electrode as claimed in claim 1, wherein the said electrode comprises a selective nanocatalyst system that is able to catalyze OER and not CER up to a reasonably high potential.
3. The electrode as claimed in claim 1 is active in the temperature range 0 to 80°C and all basic pH conditions.
4. A method for preparation of modified bi-functional electrode, comprises the following steps:
a. coating of the electrode with active material;
b. synthesis of nanocatalyst;
c. coating of the catalyst and sacrificial agent on the activated commercial
electrode to form catalyst modified electrode; and
d. applying the CN coating on the above catalyst modified electrode,
wherein the steps of synthesis of nanocatalyst followed by CN coating is
sequential or simultaneous.
5. The method as claimed in claim 4, wherein the synthesis of nanocatalyst followed by CN coating is carried out in-situ using a one-step procedure.
6. The method as claimed in claim 4, wherein the sacrificial agent first acts as a reagent and subsequently leaves by allowing a conductive coating on the surface, and
wherein the conductive coating protects the electrode without strongly affecting the HER and OER.

7. The method as claimed in claim 4, wherein the products of the said process are nanometallic nitrides/oxides/oxyhydroxides covered with a CN conductive coating.
8. The method as claimed in claim 4, wherein the synthesis of nanocatalyst comprises the following steps:
i) Surface activation via hydrothermal procedure;
ii) Coating via solution cast procedure; and
iii) Heat treatment under controlled environment,
9. The method as claimed in claim 8, wherein:
the hydrothermal treatment in the first step is carried out in the range of 30-80°C; the coating in the second step is carried out under room temperature and high-pressure conditions; and
the heating the precursor in the final step is carried out at 400°C for 3.5 h to synthesize the final catalyst.
10. A mixed metal oxide-nitride N-doped carbon coated electrode system for
catalytic application prepared with one step procedure to synthesize and coat the
catalyst on the electrode surface and apply protective coating to the catalyst
adsorbed on surface.