Covalent Organic Framework Derived Synthesis of Ru Embedded in Carbon Nitride for Hydrogen and Oxygen Evolution Reactions

The hydrogen and oxygen evolution reactions (HER and OER) are two steps in electrochemical water splitting for conversion of electric power to chemical energy. The main challenge remains the development...


Faradaic efficiency measurements for the HER and OER
In order to further assess its electrocatalytic performance toward both HE and OE reactions and support electrochemical results, faradaic efficiency (FE) measurements were also carried out on the best-performing catalyst, namely Ru@g-CNx.This was accomplished by first using gas chromatography (GC) to quantify the volume of the gas expelled under the experimental conditions.The amount of the evolved H2 is represented here as Vmeasured and the experimental setup involved 1 h of controlled potentiostatic electrolysis (CPE) with the catalyst held at +1.0 V vs. RHE (for the OER) and -1.0 V vs. RHE (for the HER).Measurements were conducted in 1.0 M KOH solutions at 25 o C.Then, using the following ratio (1), the FE value was determined: where Vcalculated stands for the theoretical volume of the gas estimated from the charge passed through the working electrode during the employed CPE under the assumption of a 100% Faradaic efficiency.
For both the HER and OER, the Faradaic efficiency values were determined using the formula presented below 1 : Where On the other hand, the Ru@g-CNx catalyst had a measured mol O2 (GC) value for the OER of 16.28 × 10 -6 mol h -1 , and the corresponding charge passed (Q) during the employed CPE was estimated to be 6.Under the same experimental conditions, the FE values of the Ru@g-CNx catalyst (99.78 and 99.73% for the HER and OER, respectively) were higher than those predicted for the commercial Pt/C (98.9% for the HER) and RuO2 (99.2% for the OER).
These results attest to the Ru@g-CNx catalyst's exceptional catalytic activity.

Figure S4 .
Figure S4.Color-coded EDS elemental maps of C, N, P and Ru in the Ru@CIN-1 sample.

Figure S10 .
Figure S10.LSV cathodic polarization curves of Ru@g-CNx in 1M KOH electrolyte solution before and after adding KSCN.

Figure S12 .
Figure S12.Faradaic efficiency measurements for both HER and OER by the best performing catalyst (Ru@g-CNx) in 1 M KOH.The electrode was held at -1.0 V vs. RHE (for the HER) and +1.0 V vs. RHE (for the OER) for 1 h in 1.0 M KOH solutions at 25 o C. The amount of the gas liberated expected from the amount of charge passed (6.15 and 6.3 C for HER and OER, respectively) assuming 100% Faradaic efficiency is shown as a solid line.The amount of the released gas detected by the GC is shown as solid spheres.

Figure S13 .
Figure S13.STEM-HAADF image of Ru@g-CNx catalyst after long term cathodic polarization with EDS mapping of Ru and O.

Table S2 .
Comparison table of Ru based electrocatalysts for HER in 1M KOH

Table S3 .
Comparison table of Ru based electrocatalysts for OER in 1M KOH

Table S4 .
Comparison table of some excellent electrocatalysts for overall water splitting in 1M KOH