Alkaline water-splitting reactions over Pd/Co-MOF-derived carbon obtained via microwave-assisted synthesis.

Cobalt-based metal-organic framework-derived carbon (MOFDC) has been studied as a new carbon-based support for a Pd catalyst for electrochemical water-splitting; i.e. , the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in alkaline medium. The study shows a high increase in the HER activity, in terms of low onset overpotential (onset η = 35 mV vs. RHE), high exchange current density ( j o,s ≈ 0.22 mA cm -2 ), high mass activity ( j o,m ≈ 59 mA mg -1 ), high kinetic current ( j K ≈ 5-8 mA cm -2 ) and heterogeneous rate constant ( k 0 ≈ 4 × 10 -4 cm s -1 ), which are attributed to the high porosity of MOFDC and contribution from residual Co, while the large Tafel slope ( b c = 261 mV dec -1 ) is ascribed to the high degree of hydrogen adsorption onto polycrystalline Pd as a supplementary reaction step to the suggested Volmer-Heyrovsky mechanism. These values for the catalyst are comparable to or better than many recent reports that adopted nano-carbon materials and/or use bi- or ternary Pd-based electrocatalysts for the HER. The improved HER activity of Pd/MOFDC is associated with the positive impact of MOFDC and residual Co on the Pd catalyst ( i.e. , low activation energy, E A ≈ 12 kJ mol -1 ) which allows for easy desorption of the H ads to generate hydrogen. Moreover, Pd/MOFDC displays better OER activity than its analogue, with lower onset η (1.29 V vs. RHE) and b a (≈78 mV dec -1 ), and higher current response ( ca. 18 mA cm -2 ). Indeed, this study provides a new strategy of designing and synthesizing MOFDC with physico-chemical features for Pd-based electrocatalysts that will allow for efficient electrochemical water-splitting processes.