Graphitic Carbon Nitride as a Catalyst Support in Fuel Cells and Electrolyzers

Pharaoh's Serpents: New Insights into a Classic Carbon Nitride Material

“…[1][2][3][4][5][6][7][8][9][10] They typically have compositions within the C-N-H system, close to that of Liebig's "melon" that has an ideal structural formula C 6 N 7 (NH)(NH 2 ), or C 2 N 3 H. [11] However, many reports equate the materials produced with pure C 3 N 4 , despite the fact that this H-free formulation has only been demonstrated in a very few instances. [12,13] This interest in producing C 3 N 4 varieties was first stimulated by theoretical predictions that an sp 3 bonded framework structure might have "superhard" properties comparable to diamond, [14] but recent research has focused on graphitic layered structures based on sp 2 bonding. [13,[15][16][17] Interestingly, it has also been predicted that open framework varieties containing mixed sp 2 as well as sp 3 bonded units could exist.…”

“…[23,24] Those investigations were initiated following Scheele's pioneering work of on prussic acid (HCN) and its salts, leading to studies of compounds containing the thiocyanate (SCN -) anion. [25] Mercurous thiocyanate was investigated by Porret, [25] whereas its mercuric counterpart, Hg(SCN) 2 , was produced by Berzelius in 1821 by reacting HgO with HSCN. [23] Based on the previous observation that cyanogen [(CN) 2 ] was formed upon heating Hg(CN) 2 , Berzelius attempted to form analogous (SCN) 2 gas by heating the thiocyanate compound.…”

“…[25] Mercurous thiocyanate was investigated by Porret, [25] whereas its mercuric counterpart, Hg(SCN) 2 , was produced by Berzelius in 1821 by reacting HgO with HSCN. [23] Based on the previous observation that cyanogen [(CN) 2 ] was formed upon heating Hg(CN) 2 , Berzelius attempted to form analogous (SCN) 2 gas by heating the thiocyanate compound. However, that experiment did not give the expected result, as large quantities of CS 2 and N 2 were evolved and HgS sublimed during the highly exothermic process.…”

“…However, that experiment did not give the expected result, as large quantities of CS 2 and N 2 were evolved and HgS sublimed during the highly exothermic process. [23] When the precursor was later mixed with elemental sulfur some (SCN) 2 was in fact produced, but the salt decomposed violently along with release of CS 2 and N 2 . Interestingly, a copious quantity of a porous, pumice-like solid was also formed, this broke open the apparatus.…”

“…Interestingly, a copious quantity of a porous, pumice-like solid was also formed, this broke open the apparatus. [23] In a separate attempt to obtain thiocyanic acid (HSCN) by treating Hg(SCN) 2 with H 2 S, Wöhler noted the characteristic snake-like appearance of the voluminous porous solid residue that emerged as the salt burned in air. [23,26] This remarkable property led to the development of pyrotechnic materials for conjuring tricks, that were first exhibited as "Serpents du Pharaon" and later sold as "Pharaoh's serpents" eggs for personal entertainment, [26] invoking a loose reference to the mystical behavior of Moses' staff.…”