The hydrogen evolution reaction (HER) and hydrogen oxidation reaction (HOR) in aqueous medium are two fundamental reactions for the development of non-fossil energy storage and conversion devices. In the polymer electrolyte membrane fuel cell (PEMFC) carbon supported platinum (Pt/C) based catalysts are universally used in cathodes and anodes; however, the poor durability of Pt/C due to degradation of the catalyst in the strongly oxidizing environment prevents its widespread applications. It remains a great challenge to develop new electrocatalysts with superior activity and very high durability for the HER/HOR. Here, we report the synthesis of a porous palladium nanoparticle− carbon nitride composite (Pd-CN x ) for its superior activity and high durability toward the HER/HOR in acidic and alkaline media. The Pd-CN x composites exhibited high catalytic activity for hydrogen evolution in acidic media with a small onset potential of −12 mV and a Tafel slope of 35 mV dec −1 . At a small Pd loading of 0.043 mg cm −2 , this catalyst also exhibits a current density of 10 mA cm −2 at a low overpotential of −55 mV with an excellent stability. The HER activity on Pd-CN x composite is comparable to that of commercial Pt/C in acid media. The stability tests of this catalyst were done through a large number of repeated potential cycles and long-term electrolysis. These confirm the exceptional durability of this catalyst, which is much better than that of Pt/C catalysts. Furthermore, this catalyst has also displayed superior HOR activity, measured by a rotating-disk experiment with a broad range of pH (0−14) in different buffer solutions. The HER/HOR activities of porous Pd-CN x composite in different buffer solutions were correlated with the hydrogen binding energy (HBE) of the catalyst surface. The HER/HOR activity gradually decreases with an increase in the HBE as the solution pH increases. The superior HER/HOR activities and very high durability at porous Pd-CN x composite are due to strong bonding between Pd and carbon (Pd−C bond), the porous morphology, and synergistic interactions between Pd-NPs and the carbon nitride (CN x ) support.

Development of highly efficient and durable bifunctional electrocatalyst for hydrogen and oxygen evolution reactions (HER and OER) is essential for efficient solar fuel generation. The commercial RuO or RuO-based catalysts are highly active toward OER, but their poor stability under different operating conditions is the main obstacle for their commercialization. Herein, we report growth of one-dimensional highly crystalline RuO nanowires on carbon nitride (1D-RuO-CN) for their applications in HER and OER at all pH values. The 1D-RuO-CN, as an OER catalyst, exhibits a low onset overpotential of ∼200 mV in both acidic and basic media, whereas Tafel slopes are 52 and 56 mV/dec in acidic and basic media, respectively. This catalyst requires a low overpotential of 250 and 260 mV to drive the current density of 10 mA cm in acidic and basic media, respectively. The mass activity of 1D-RuO-CN catalyst is 352 mA mg, which is ∼14 times higher than that of commercial RuO. Most importantly, the 1D-RuO-CN catalyst has remarkably higher stability compared to commercial RuO. This catalyst also exhibits superior HER activity with a current density of 10 mAcm at ∼93 and 95 mV in acidic and basic media. The HER Tafel slopes of this catalyst are 40 mV/dec in acidic condition and 70 mV/dec in basic condition. The HER activity of this catalyst is slightly lower than Pt/C in acidic media, whereas in basic media it is comparable or even better than that of Pt/C at higher overpotentials. The HER stability of this catalyst is also better than that of Pt/C in all pH solutions. This superior catalytic activity of 1D-RuO-CN composite can be attributed to catalyst-support interaction, enhanced mass and electron transport, one-dimensional morphology, and highly crystalline rutile RuO structure.

Fabrication of high surface area interconnected porous network of metallic nanomaterials is important for their applications in various fields such as catalysis, sensors, and electrochemistry. Here we report a facile bottom up synthesis of high surface area and porous, gold aerogel supported on carbon nitride sheets (CNx). The reduction of HAuCl4 in presence of carbon nitride nanosheets using sodium brohydride and ultrasonic treatment produces gold aerogel supported on carbon nitride (Au-aerogel-CNx). When the reduction of HAuCl4 in presence CNx nano sheets was done only with ultrasonication, highly dispersed ultra small ( ~2 nm) gold nanoparticles on CNx sheets (AuNPs-CNx) were formed. The Au aerogel supported on CNx sheets was well characterized by powder X-ray diffraction, tunneling electron microscopy, selected area electron diffraction, energy dispersive X-ray spectroscopy, scanning electron microscopy, UV-Visible and Xray photo electron spectroscopic methods. The Au-aerogel-CNx and AuNPs-CNx composites exhibited superior electro catalytic activity towards oxygen reduction reaction (ORR) in alkaline and acidic media. The Au-aerogel-CNx composite show ORR onset potentials at 0.92 V and 0.43 V (Vs RHE) in 0.5 M KOH and H2SO4 solution. The four electron oxygen reduction proceess occurs at these supported catalysts in both alkaline and acidic media. In alkaline (KOH) medium the onset potential at Au-aerogel-CNx is more positive ( ~ 30 mV) than that of commercial Pt/C catalyst. The composites display excellent methanol tolerance and comparable durability with commercial Pt/C. Furthermore, the Au-aerogel-CNx composites exhibited high catalytic activity for hydrogen reduction reaction (HER) with small onset potential of -30 mV and a Tafel slope of 53 mV dec -1 in acidic medium. At a small Au loading of 0.130 mg cm -2 , this catlyst also exhibit a current density of 10 mA cm -2 at a low overpotential of -185 mV with an excellent stability. The ORR and HER performaneces on porous, Au-aerogel-CNx composites is better than that of AuNPs-CNx catalyst and commercial flat gold electrode. The superior ORR and HER activity at Au-aerogel-CNx composite are originated from the unique synergistic effects between porous Au network and carbon nitride (CNx) support. Please do not adjust margins Please do not adjust margins approaches are available in literature for synthesis of different non metal aerogel such as carbon aerogel 11 , silica aerogel 12 , organic-inorganic hybrid 13 , metal oxide 14 , and metal chalcogenides 15 . But only few methods are available for the production of metal aerogel 8,16,17,18 . For example, Eychmüller and coworkers 8,16 have reported synthesis for monometallic, bi-metallic and composite aerogels based on controlled aggregation of metal nanoparticles using controllable destabilization and spontaneous gelation methods. Leventis and his co-workers 17,18 developed methods for synthesis of different metallic (Fe, cu, Ni, Co) aerogels by nanosmelting (sol-gel method) of hybrid polymer-metal oxide composit...

Rh–Rh2O3 nanostructures exhibit superior HER and HOR in acid and base; hydrogen binding energy and oxophilicity were found to be the equivalent descriptors for HER/HOR in alkaline medium.

Finding nonprecious metal based highly active and durable bifunctional electrocatalysts for overall water-splitting is essential for the development of various renewable energy storage and conversion technologies. Herein, we report the synthesis of cobalt iron layered double hydroxide (Co 1−δ Fe δ LDH) and g-carbon nitride composite (Co 1−δ Fe δ LDH/g-CN x ) for alkaline water electrolysis. The thin Co 1−δ Fe δ LDH nanosheets are successfully impregnated on graphitic carbon nitride surface by one pot co-precipitation method at ambient temperature. The optimal composite, Co 0.4 Fe 0.6 LDH/g-CN x exhibited superior OER activity in 1 M KOH electrolyte with a small overpotential of 0.28 V for 10 mA cm −2 , low Tafel slope of 29 mV/dec, 100% faradic efficiency, and high TOF of 0.25 s −1 which is superior to commercial (comm) IrO 2 . Furthermore, the Co 0.4 Fe 0.6 LDH/g-CN x composite also exhibited remarkable HER activity in alkaline media and its HER activity is slightly lower than that of comm Pt/C at low overpotential but it outperforms Pt/C at high overpotential. The catalyst demonstrated its long-term durability and higher stability for HER and OER under alkaline environment. This Co 0.4 Fe 0.6 LDH/g-CN x catalyst can serve as both cathode and anode for overall water-splitting and required the small potential of 1.61 V to achieve a current density of 10 mA cm −2 . The superior electrocatalytic activities of the Co 0.4 Fe 0.6 LDH/g-CN x composite are due to the high electrochemical surface area (ECSA), easy access of abundant active sites, and easy mass transport owing to 2D sheet morphology of the composite.