Approach to Evaluation of Electrocatalytic Water Splitting Parameters, Reflecting Intrinsic Activity: Toward the Right Pathway

Abstract

The development of transition metal‐based non‐precious‐metal electrocatalysts for energy storage and conversion systems has received a lot of interest recently. To further this subject in the proper way given the development of electrocatalysts, a fair comparison of their respective performance is necessary. This Review investigates the parameters used for the comparison of electrocatalyst activity. Significant evaluation criteria employed in electrochemical water splitting studies are the overpotential at defined current density usually at 10 mA per geometric surface area, Tafel slope, exchange current density, mass activity, specific activity and turnover frequency (TOF). This Review will discuss how to identify the specific activity and TOF by electrochemical and non‐electrochemical methods to represent intrinsic activity as well as the benefits and uncertainties of each technique, ensuring that each method is applied correctly when calculating intrinsic activity metrics.

Tuning the heterophase junction in Bi2O3 hybrid crystals with enhanced photocatalytic activity

“…The observations herein are consistent with the previous Nyquist results. In addition, the double-layer capacitance ( C dl ) is linearly proportional to the number of active surface sites, and the equation below yields the value of C dl : 57 Δ J = v × C dl Δ J stands for the difference between anodic and cathodic current densities at the middle potential (0 V vs. Ag/AgCl), and v represents the scan rate. In Fig.…”

Three-Dimensional Network of Highly Uniform Cobalt Oxide Microspheres/MXene Composite as a High-Performance Electrocatalyst in Hydrogen Evolution Reaction

“…The linear slope is equal to twice the value of the double-layer capacitance C dl . To calculate the turnover frequency (TOF), we used the formula T O F = J N A n F normalΓ where J (A cm –2 ) is the current density, N A is the Avogadro number (6.022 × 10 23 molecules per mol), n is the number of electrons involved in the evolution of the H 2 molecule, F is the Faraday constant (96,485 C mol –1 ), and Γ is the number of participating atoms in the catalyst material. We determined a minimum (TOF bulk ) and a maximum (TOF surface ) TOF based on two different assumptions (Supporting Information) on the number of active sites.…”

“…ECSA may be used for the purpose of comparing the activity patterns shown by catalysts within the same research. 49 The pure non-Faradaic response is evident in the pseudorectangular forms shown in Figures S6 and 4e The TOF was used to assess the intrinsic activity, which refers to the rate of H 2 generation per active site per unit of time. Two distinct estimates were used to determine the total number of active sites (Supporting Information).…”

‘Total electrode’ and ‘intrinsic’ activity parameters in water electrolysis: a comprehensive investigation

“…The loading of the catalyst over the current collector largely governs the catalytic activity toward the OER or other applications. 13 For a certain catalyst the respective polarization curves with different mass loadings show different current densities for the reaction of concern (Fig. 5a).…”

“…7 Nazari et al have described the overpotential at a predefined current density (at 10 mA cm −2 ); the Tafel slope, exchange current density, mass activity, specific activity, and turnover frequency (TOF) are important evaluation criteria used in electrochemical water splitting research. 13 Despite such reports where the importance of using various intrinsic activity parameters is highlighted, in most reports, there is still the nonexistence of these intrinsic parameters. This might be due to a lack of proper and compact experimental support while distinguishing two sets of activity parameters.…”