# Noble Metal-Based Heterogeneous Catalysts for Electrochemical Hydrogen Evolution Reaction
## 2 Factors That Affect HER Performance
### Influence of the Working Electrode  
In order to characterize the intrinsic catalytic activity as close as possible to the catalytic material, the preparation of working electrodes is of great importance in basic laboratory research. The working electrode refers to the electrode that can cause significant changes in the concentration of the components to be measured in the test solution during the test process, such as a glassy carbon electrode and platinum electrode. Generally, the bubbles generated on the electrode surface easily adhere to the surface of the catalyst, which makes the electrolyte mass transfer difficult. To solve this problem, [PERSON] et al. first developed a high-speed rotating electrode, namely the RDE (Rotating Disk Electrode) [38]. Later, it was popularized by [PERSON] et al. [39] using ink injection electrodes. Under high-speed rotation, the adverse effect of a large number of bubbles on the surface of the catalytic material is eliminated. The RDE is applicable to the three-electrode system. Figure 3a shows five electrolytic cells. The largest port in the middle is the working electrode and the rotating rod, while the other four ports are the counter electrode, the reference electrode, the air inlet (the required saturated gas should be passed into the electrolyte before the test) and the air outlet, and the placement position is not required [14]. The most common configuration of the RDE is a Teflon shell (length: 27 mm, diameter: 15 mm) wrapped with a glassy carbon electrode (diameter: 5 mm); the conductive flat glass carbon electrode on the RDE end face is used as a collector. The drip method is used to uniformly cover the glass carbon with the highly dispersed catalyst slurry prepared by the catalysts, binders and solvent. Some researchers also use carbon cloth, nickel foam and other rough substrate-supported catalysts with higher specific surfaces to improve stability. Although these are feasible paths, the substrate itself will have a better or worse effect on the catalytic performance [40]. The catalyst ink is generally composed of a catalyst with mass fraction \(w\) = 0.5-1.2%, deionized water with \(w\) = 0.6-1.1%, Nafion binder with \(w\) = 0.9-1.3% and solvent with \(w\) = 90-99% (including ethanol, isopropyl alcohol, n-propyl alcohol or n-butanol in any one or more combinations). The conventional preparation process is as follows: the catalyst, deionized water, solvent and binder are added into glass bottles or centrifugal tubes and then mixed with ultrasonic for 30-60 min until it is uniform to obtain catalyst slurry. Considering the mass transfer problem, the amount of catalyst should be appropriate, and the amount of Nafion should be as little as possible [41]. In addition, the electrode preparation of some catalyst particles requires the addition of a conductive agent (without significant interference to the structure or properties of the catalyst). For the HER, high specific surface area carbon (such as TKK, Vulcan or Ketjen Black) is a good choice. Conductive additives can disperse catalyst particles to avoid agglomeration and ensure fast electron transport. For the HER, the commercial Pt/C catalyst is often used for comparison samples, which is made with 46 wt% Pt loaded on high specific surface area carbon TKK (Tanaka Kikinzoku, Kogyo, Japan). The preparation was as follows: the glassy carbon electrode was polished with 0.05 \(\upmu\)m alumina paste (initially large, then reduced to 0.05 \(\upmu\)m) to achieve a mirror finish, cleaned repeatedly with ultrasonic waves in deionized water and dried for use under ambient conditions. The Pt/C and Nafion binders were dispersed in deionized water (18.2 M\(\Omega\) cm, Millipore) and then treated with ultrasound in an ice bath for 30 min to obtain a homogeneous catalyst ink consisting of 0.15 mgPt/C mL\({}^{-1}\) and 0.04 mgNafion mL\({}^{-1}\). The RDE (diameter: 5 mm) was uniformly coated with 20 \(\upmu\)L ink to obtain a platinum loading capacity of \(\sim\)7.0 \(\upmu\)gPt cm\({}^{-2}\)disk. [42].