Pt wire

Electrochemical impedance measurements were performed with an Electrochemical Analyzer 600E (CH Instruments Inc., USA) using a conventional three-electrode cell. An Ag/AgCl wire (saturated in KCl) (CH Instruments Inc., USA) was used as a reference electrode, and a Pt wire (CH Instruments Inc., USA) was used as a counter electrode. The scaffolds as working electrodes were held inside the electrolyte using an alligator clip outside the liquid surface and connected to the wiring. Impedance measurements were performed in a 1 M KCl solution with an AC bias sweeping in a frequency range of 40 Hz to 1 MHz, with an amplitude of 5 mV (n = 3).

Fluorine-doped tin oxide (FTO) (1.5 × 2 cm²) was used as a substrate to support samples (10 mg) that were ultrasonically dispersed in 20 mL ethanol and then added dropwise to coat the FTO. The sample loaded FTO was then dried at 60 °C for 2 h and a 1.5 × 1.5 cm² sample area was used for the photoexcitation experiment.
The photocurrent was measured on a CHI 660E electrochemical workstation with a three-electrode system, in which the prepared electrode was used as the working electrode, a Pt wire (CH Instruments, Inc.) was used as the counter electrode, and a Ag/AgCl (CH Instruments, Inc.) electrode was used as the reference electrode. A 0.5 M Na₂SO₄ solution was used as the electrolyte. A Xe lamp (CEL-HXF300, CEAULIGHT) with AM 1.5 filter (CEL-AM 1.5, CEAULIGHT) was used as the light source. The light intensity was regulated to 50 mW·cm⁻² by adjusting the distance between the light source and the sample.

Red phosphorous powder (Sigma-Aldrich, ≥97%, CAS No. 7723-14-0), Iron(III) nitrate nonahydrate [Sigma-Aldrich, Fe(NO₃)₃·9H₂O, ≥99.95%, CAS No. 7782-61-8], Pt wire (CH Instruments, Inc.), Nafion 117 solution (5%; Sigma-Aldrich), iridium oxide powder (Alfa Aesar, IrO₂, 99%), potassium hydroxide (Alfa Aesar, KOH, 50% wt/vol), and Ni foam (areal density 320 g cm⁻²) (ref. ^{2 (link)}) were used without further purification.

The electrochemical measurements were conducted in a three-electrode setup with an electrochemical station (Gamry, Reference 600). The polarization curves were collected by linear sweep voltammetry with a scan rate of 0.5 mV s⁻¹ in 82 ml of 0.5 M H₂SO₄, so as to suppress the capacitive current due to the high surface area and high porosity of the porous samples38 (link). A saturated calomel electrode was used as the reference electrode, a Pt wire (CH Instruments Inc.) as the counter electrode and as-prepared hybrid catalysts as the self-supported working electrodes. During the electrochemical measurements, high-purity N₂ gas was continually bubbled throughout the whole electrochemical measurement. Potentials versus RHE can be calculated compared with saturated calomel electrode by adding a value of 0.263 V after calibration. The electrochemical stability of the catalyst was evaluated by continuously cycling the catalyst for 1,000 times at a scan rate of 50 mV s⁻¹. Chronoamperometry was performed under a given potential for the MoS_2(1−x)Se_2x/NiSe₂ hybrid electrode. The electrochemical impedance spectroscopy test was carried out in the same device configuration at a potential of −0.15 V versus RHE with the frequency ranging from 10 mHz to 1 MHz with a 10 mV AC dither. All the potentials used here were referred to RHE.