Silicon Atom Doping in Heterotrimetallic Sulfides for Non-noble Metal Alkaline Water Electrolysis

The engineering of a pentlandite (Fe3Co3Ni3S8, FCNS) doped with silicon (FCNSSi) for water splitting is demonstrated. At 500 mA cm−2, a two-electrode zero-gap cell assembly demonstrates the FCNSSi catalyst's promise for practical applications.


The overall electrochemical water spitting test on FCNSSi
The results presented here clearly demonstrate that the FCNSSi electrode is a highly active and stable bifunctional electrocatalyst for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER).To investigate its potential for overall water splitting, we designed a two-electrode cell in which FCNSSi served as both anode and cathode in an alkaline solution (see inset in Figure S15a).The FCNSSi electrode showed impressive activity, achieving a water-splitting current density of 10 mA cm -2 at a potential of 1.66 V.This represents a significant reduction in overpotential of 260 mV compared to the pristine FCNS electrode (1.92 V), and is comparable to previously reported non-noble bifunctional electrocatalysts for water splitting [1] .
Furthermore, a chronopotentiometry test conducted at 100 mA cm -2 for 24 hours confirmed the high stability of the FCNSSi electrode with an overall cell potential of 2.19 V, indicating its potential for practical application in overall water splitting in an alkaline environment (Figure S15b).

Figure S16
Chronopotentiometry test of FCNSSi/CPE at 200 mA cm -2 in 1.0M KOH for three executive days.
Remarkably, the FCNSSi electrode exhibited efficient and stable water-splitting performance for three consecutive days at 200 mA cm -2 , with a decrease in the overall cell potential from 2.49 V to 2.41 V (Figure S16).Overall, these findings demonstrate the promising potential of the FCNSSi electrode as an efficient and stable electrocatalyst for overall water splitting in alkaline solutions, making it a strong candidate for practical application in various renewable energy conversion and storage systems.Table S3 HER performance of our materials against the previously reported pentlandites electrocatalysts.Table S4 FE% of our materials against the previously reported pentlandites electrocatalysts for HER.

Figure S4
Figure S4High-resolution XPS spectra of S 2p, and Si 2p orbitals collected from wide scan survey of FCNSSi-RT sample.

Figure S5 a
Figure S5 a) Nitrogen gas sorption isotherms, and b) average pore size distribution curves of FCNS, FCNSSi, and FCNSSi-RT powders.

Figure S6
Figure S6 CV curves a,c) at 10, 20, 40, 60, 80, 100, and 150 mV s -1 in 1.0 M KOH solution and b,d) double layer charging current vs. scan rate plots of pristine FCNS and doped FCNSSi on classy carbon electrode to determine ECSA.

Figure S7
Figure S7 Gas chromatograms (GC) of oxygen determination during# 1h of OER performance at 20 mA cm -2 .

Figure S8 a
Figure S8 a) Chronopotentiometry measurements of our materials on carbon paper electrode at 100 mA cm -2 for 24h, and b) PXRD patterns of FCNSS/CE before and after chronopotentiometry test at 100 mA cm -2 for 24h.

Figure S9
Figure S9 EDX spectra of the FCNSSi sample on carbon paper electrode after chronopotentiometry test at 100 mA cm -2 for 24h.

Figure S10
Figure S10 a) SEM image and the corresponding atoms mapping (Fe, Co, Ni, S, Si, O, and Cl), and b) EDX spectra of FCNSSi-RT powder sample.

Figure S11 a
Figure S11 a) PXRD pattern of FCNSSi-RT powder and LSV curves in b) 1.0 M KOH and c) 0.5 M H2SO4 of FCNSS-RT sample at a scan rate of 50.0 mV s -1 on glassy carbon electrode (GCE).

Figure S12
Figure S12 Top view of optimized the metal octahedral site (Fe, Co and Ni) in FCNSSi surface covered with 7/4 O* ML.

Figure S13
Figure S13 Gas chromatograms for hydrogen determination during 1h of HER performance at -20 mA cm -2 , and b) the calculated faradic efficiency percentage (FE%).

Figure S14
Figure S14PXRD of FCNSSi/CE before and after chronopotentiometry test at -20 mA cm -2 for 10 h in argon.

Figure S15 a
Figure S15 a) LSV curves for the overall water splitting using FCNS and FCNSSi at both cathode and anode at a scan rate of 10 mV s -1 in 1.0 M KOH solution.b) Chronopotentiometry test of bare CPE, pristine FCNS, and FCNSSi electrodes at 100 mA cm -2 .

Figure S17
Figure S17 a) Top view of optimized (111) pristine FCNS surface, b) Top view of optimized (111) Si adsorbed on FCNS surface (FCNSSi-RT), c) Top view of optimized (111) FCNS surface doped Si (FCNSSi), d) Top view and side view of hydrogen adsorption on FCNSSi.

Figure
Figure S18 a) LSV curves and b) chronopotentiometry test at 500 mA cm -2 for 10 h collected using zero-gap cell in 1.0M KOH and using a FumaSep AEM.

Figure
Figure S19 a) Zero-gap cell assembly using FCNSSi on CPE at cathodic side against Ni foam at anodic side, and b) chronopotentiometry test at -100 mA cm -2 for 10 h and the estimated FE% for HER.

Table S1
Atomic percentage of elements in our materials determined by ICP-OES analysis.

Table S2
OER performance of our materials against the previously reported pentlandites electrocatalysts.