Question: For which invention are both Christian Friedrich Schönbein, a the German-Swiss chemist and William Robert Grove, the Welsh judge and physical scientist given credit?

full_context: Document 1: William John Macquorn Rankine: William John Macquorn Rankine, {'1': ", '2': ", '3': 'FRSE FRS', '4': "} ( ; 5 July 1820 – 24 December 1872) was a Scottish mechanical engineer who also contributed to civil engineering, physics and mathematics. He was a founding contributor, with Rudolf Clausius and William Thomson (Lord Kelvin), to the science of thermodynamics, particularly focusing on the first of the three thermodynamic laws.
Document 2: Christian Friedrich Schönbein: Christian Friedrich Schönbein (18 October 1799 – 29 August 1868) was a German-Swiss chemist who is best known for inventing the fuel cell (1838) at the same time as William Robert Grove, Robert Cumming and his discoveries of guncotton and ozone.
Document 3: William Gilbert (astronomer): William Gilbert ( ; 24 May 1544 – 30 November 1603), also known as Gilberd, was an English physician, physicist and natural philosopher. He passionately rejected both the prevailing Aristotelian philosophy and the Scholastic method of university teaching. He is remembered today largely for his book "De Magnete" (1600), and is credited as one of the originators of the term "electricity". He is regarded by some as the father of electrical engineering or electricity and magnetism.
Document 4: Robert Boyle: Robert William Boyle {'1': ", '2': ", '3': ", '4': "} (25 January 1627 – 31 December 1691) was an Anglo-Irish natural philosopher, chemist, physicist and inventor born in Lismore, County Waterford, Ireland. Boyle is largely regarded today as the first modern chemist, and therefore one of the founders of modern chemistry, and one of the pioneers of modern experimental scientific method. He is best known for Boyle's law, which describes the inversely proportional relationship between the absolute pressure and volume of a gas, if the temperature is kept constant within a closed system. Among his works, "The Sceptical Chymist" is seen as a cornerstone book in the field of chemistry. He was a devout and pious Anglican and is noted for his writings in theology.
Document 5: Peter Desaga: Peter Desaga was a German instrument maker at the University of Heidelberg who worked with Robert Wilhelm Bunsen. In 1855, Desaga perfected an earlier design of the laboratory burner by Michael Faraday into the Bunsen burner. The Desaga family held the right to market the burner for generations, as part of an agreement made with Bunsen. The Bunsen burner was essential to the invention of the spectroscope by Robert Wilhelm Bunsen and Gustav Robert Georg Kirchhoff.
Document 6: Rudolf Christian Böttger: Böttger was born in Aschersleben, Germany in 1806. After attending the primary school there he joined the school of the Franksche Stiftung in Halle an der Saale at the age of eleven. In 1824, Böttger started to study theology, but in parallel also attended the science lectures at the University Halle. The lectures of Johann Salomo Christoph Schweigger had a strong influence on him. Böttger left the university in 1828 and worked as cleric and teacher at different locations. The contact with Schweigger never faded and in 1831 Böttger decided to leave the theology career. He was offered a job at the voluntary association for chemistry in Frankfurt in 1835. His first major work in Frankfurt was the improvement of the electrotyping method for the production of printing plates. Böttger received his PhD from the University of Jena in 1837 and was appointed as full professor in Frankfurt in 1842. Böttger married Christiane Harpke in 1841, and they had eight children. He and Christian Friedrich Schönbein, a German-Swiss chemist, discovered nitrocellulose independently in 1846. Both scientists collaborated to earn money with the invention, but they were not successful. The development of the safety match in 1848 and the synthesis of the first organocopper compound, the explosive copper(I) acetylide CuC in 1859 were examples for his chemistry research. Böttger stayed at the University of Frankfurt am Main for the rest of his life, although he was offered positions at other universities. He died of a liver illness in 1881.
Document 7: James Graham (sexologist): James Graham (1745–1794) was a Scottish proponent of electrical cures, showman, and pioneer in sex therapy. A self-styled doctor, he was best known for his electro-magnetic musical Grand State Celestial Bed. Dismissed as a quack by medical experts, Graham apparently believed in the efficacy of his unusual treatments.
Document 8: William Robert Grove: Sir William Robert Grove, PC, FRS FRSE (11 July 1811 – 1 August 1896) was a Welsh judge and physical scientist. He anticipated the general theory of the conservation of energy, and was a pioneer of fuel cell technology. He invented the Grove voltaic cell.
Document 9: Nikolay Zelinsky: Zelinsky studied at the University of Odessa and at the universities of Leipzig and Göttingen in Germany. Zelinsky was one of the founders of theory on organic catalysis. He is the inventor of the first effective filtering activated charcoal gas mask in the world (1915).
Document 10: Archibald Grove: Thomas Newcomen Archibald Grove (1855 – 4 June 1920), commonly known as Archibald Grove, was a British magazine editor and Liberal Party politician.
Document 11: Charge conservation: In physics, charge conservation is the principle that electric charge can neither be created nor destroyed. The net quantity of electric charge, the amount of positive charge minus the amount of negative charge in the universe, is always "conserved". Charge conservation was first proposed by British scientist William Watson in 1746 and American statesman and scientist Benjamin Franklin in 1747, although the first convincing proof was given by Michael Faraday in 1843.
Document 12: Grove cell: The Grove cell was an early electric primary cell named after its inventor, Welsh physical scientist William Robert Grove, and consisted of a zinc anode in dilute sulfuric acid and a platinum cathode in concentrated nitric acid, the two separated by a porous ceramic pot.
Document 13: Explosions-Polka: Explosions-Polka, op. 43, is a polka written by Johann Strauss II in 1847. The title was inspired by a discovery of guncotton or nitrocellulose by German scientist Christian Friedrich Schönbein in 1840. The Viennese press eagerly reported this discovery many years later in 1846, describing many products that can then be made 'explosive'.
Document 14: United States hydrogen policy: The principle of a fuel cell was discovered by Christian Friedrich Schönbein in 1838, and the first fuel cell was constructed by Sir William Robert Grove in 1839. The fuel cells made at this time were most similar to today's phosphoric acid fuel cells. Most hydrogen fuel cells today are of the proton exchange membrane (PEM) type. A PEM converts the chemical energy released during the electrochemical reaction of hydrogen and oxygen into electrical energy. The Energy Policy Act of 1992 was the first national legislation that called for large-scale hydrogen research. A five-year program was conducted that investigated the production of hydrogen from renewable energy sources and the feasibility of existing natural gas pipelines to carry hydrogen. It also called for the research into hydrogen storage systems for electric vehicles and the development of fuel cells suitable to power an electric motor vehicle.
Document 15: Robert Bunsen: Robert Wilhelm Eberhard Bunsen ( ; ] ; 30 March 1811 – 16 August 1899) was a German chemist. He investigated emission spectra of heated elements, and discovered caesium (in 1860) and rubidium (in 1861) with the physicist Gustav Kirchhoff. Bunsen developed several gas-analytical methods, was a pioneer in photochemistry, and did early work in the field of organoarsenic chemistry. With his laboratory assistant, Peter Desaga, he developed the Bunsen burner, an improvement on the laboratory burners then in use. The Bunsen–Kirchhoff Award for spectroscopy is named after Bunsen and Kirchhoff.
ground_truth: fuel cell