Table 1 lists the detailed information of this dataset, including the title, authors, data generation time, data format etc.

The dataset presents here is generated from a systematic study of the Ni and Co-based phosphides towards the electrocatalytic OER in alkaline media. The phosphides were synthesized using low-temperature solvothermal method or an electrodeposition method. The data serve as the benchmark for the OER activity of metal phosphide-type materials (Table 2), with the corresponding compositions detailed in Table 3. In Table 2, key parameters in evaluating the OER performance of electrocatalysts are given, including overpotential at 10 mA/cm² (η₁₀), Tafel slope, number of electrochemically active atoms, double layer capacitance (C_dl), and charge transfer resistance (R_ct). The η₁₀ is a widely accepted parameter in the area of OER. A lower η₁₀ indicates superior OER activity. Tafel slope and R_ct values are related to the OER kinetics. Generally, lower Tafel slope values and R_ct values indicate the more favorable kinetics and thus higher catalytic OER activity. Besides, the mechanism of OER can be inferred from the Tafel slope values. The number of electrochemically active atoms and C_dl are related to the number of active sites of the catalysts. Furthermore, users can use the data to compare the OER activity of metal phosphides that are synthesized with variations in methods, surface structures, metal doping, crystallinity and other properties. The format of these data includes .bin (original data file generated using CHI software), .opj (Origin project file), .txt (text file), and .csv (spreadsheet file), which can be easily plotted to compare with the user’s experimental results. Through activity comparison and key electrochemical parameter analyses, reasons for the inferior or superior OER activity can be inferred to aid the rational design of more efficient metal phosphide-based electrocatalysts for alkaline OER reaction.

The data were generated using a CHI 660E potentiostat, with the corresponding software developed by the company. The original data was stored as .bin format. To generate the data, metal phosphide nanostructures were synthesized using the solvothermal phosphidization or electrodeposition method described later. For the samples synthesized using the solvothermal phosphidization method, the working electrode was prepared by drop-casting of an ink that contains the metal phosphide samples. The substrate used was a piece of cleaned nickel foam or carbon paper. Inks were prepared by dispersing certain amounts of powdery sample in water or water/ethanol mixed solvent, with 1% Nafion ionomer added as the binder.

After sonication for 20 min, appropriate amounts of inks were dropped onto the substrate surface to cover 1 cm² geometric area, to achieve the loading of the metal phosphide on the electrode surface at about 1 mg/cm². For the samples synthesized using the electrodeposition method, no ink was required to prepare the working electrode, as the electrodeposition method was used to generate a thin layer of metal phosphides at the substrate surface with good adhesion. The loading for the electrodeposited film is higher, typically at around 2 mg/cm². The OER activity was measured, and cyclic voltammogram (CV) and electrochemical impedance spectroscopy were performed using the three electrode setup. Approximately 1 cm² geometric surface area of the working electrode was immersed in the 1 mol/L KOH electrolyte. The counter electrode was a cleaned graphite rod, and the reference electrode was a saturated calomel electrode (SCE). The electrochemical measurements were carried out at room temperature. The CV was scanned for 20 cycles in the potential region of 0−0.6 V vs. SCE to activate the working electrode till a stable CV was acquired. Then anodic or cathodic linear sweep voltammetry (LSV) was applied at 1, 2 or 5 mV/s covering the OER region. The overpotential of OER at a certain current density was acquired following the Equation (1),where E_RHE is the acquire potential in the reversible hydrogen scale and 1.229 V is the standard redox potential for OER. The Tafel slope value (b) is acquired by plotting the LSV curve in the OER region following Equation (2),where a is a constant, and j is the current density. To acquire the number of electrochemically active sites (n), CV at 50 mV/s is acquired covering the redox of Ni^2+/3+ peaks or Co^2+/3+ peaks. The total charge (Q) for the reduction peak is integrated. Following Equation (3), n can be acquired.where F is the Faraday constant, and z is the number of electrons transferred in the redox processes (assumed to be 1). In some cases where the redox peaks are unable to be identified, the C_dl was used to estimate the number of surface active sites. CVs in the non-Faradaic region were collected at different scan rates. By plotting the difference between anodic current and cathodic current against the scan rate, the slope yields the C_dl value. The electrochemical impedance data were acquired at the applied potential corresponding to the η at 10 mA/cm², with the alternating potential amplitude at 10 mV and the frequency range in 10⁵−0.01 Hz. The solution resistance ranged from 0.5 to 1 Ω, and the LSV data were iR-corrected using the solution resistance value for each sample. The R_ct value is acquired from the impedance data.

The crystallinity of the metal phosphides was acquired using a Rigaku Smartlab 9 kW Diffraction System using a Cu Kα source (λ = 0.15406 nm). The composition of the metal phosphides was determined using the inductively coupled plasma-atomic emission spectroscopy (ICP-AES) with an iCAP 7400 analyzer. The measurement conditions are as follows: forward power 1350 W, plasma gas flow rate 12.0 L/min, nebulizer gas flow rate 1.0 L/min, auxiliary gas flow rate 1.0 L/min, sample uptake speed 50 r/min with white/orange Tygon tubing. A concentric nebulizer was used with a cyclonic spray chamber. ICP-AES analysis was performed without an internal standard. Each value was measured three times, and the results are reported in the form of mass ratio and atomic ratio in Table 3.

The data provided in this database include LSV, CV, and electrochemical impedance data. For NiP-1 to NiP-19, CoP-1 to CoP-7 and CoP-9 to CoP-11, the samples were synthesized using the solvothermal phosphidization method^{[1−4,6−9]}. These samples are powdery with nanostructures. The general procedure of this solvothermal phosphidization method is as follows: MOF (0.2 g) was dispersed in 30 mL N, N-dimethylformamide (DMF). Then 0.15 g white phosphorus (P₄) was added, and the suspension was transferred into a 50 mL Teflon-lined stainless-steel autoclave. The autoclave was heated at 160 °C for 14 h, and the black precipitates were collected, washed with water, ethanol, and benzene, and dried. All these samples were synthesized following this typical procedure with slight modification as detailed below. NiP-1 to NiP-4 were prepared with NiFe-BTC (trimesic acid) MOF, where different amounts of Ni and Fe exist in the MOF. NiP-6, NiP-7 and NiP-8 were prepared by reacting 0.1 g Ni-BTC MOF with 0.025, 0.065 and 0.105 g P₄, respectively. NiP-9 to NiP-11 were heterostructures of Ni₂P/FeOOH, where Ni₂P was formed using the solvothermal phosphidization method using 0.1 g Ni-BTC MOF and 0.065 g P₄. Then, 0.02 g Ni₂P was dispersed in 20 mL of water and ethanol with 0.17, 1.33 and 6.67 mg/mL FeCl₃ 6H₂O for 4 h at room temperature to form NiP-9, NiP-10 and NiP-11, respectively. NiP-12 and NiP-13 were synthesized using NiFe-BTC-MOF and Ni-BTC MOF with 0.6 mmol P₄ at 180 °C for 12 h. NiP-14, NiP-15 and NiP-16 were synthesized using 0.3 g FeCoNi-BPDC (biphenyl-4,4′-dicarboxylic acid)-MOF, NiFe-BPDC-MOF, and NiCo-BPDC-MOF, respectively, and 0.27 g P₄. NiP-17, NiP-18 and NiP-19 were synthesized using 0.1 g Ni-BDC (1,4-dicarboxybenzene), Ni-BPDC and Ni-NDC (2,6-naphthalenedicarboxylic acid) MOF, respectively, with 0.065 g P₄. CoP-1 to CoP-4 were synthesized using CoFe-BTC-MOF with different Co to Fe ratios, with 0.09 g P₄ in DMF/ethylene glycol (v∶v = 1) solvent at 170 °C for 16 h. CoP-5, CoP-6 and CoP-7 were synthesized using Co-BTC-MOF with 0.09 g P₄ in DMF/ethanol, DMF and DMF/glycerol (v∶v = 1) solvents, respectively, at 170 °C for 16 h. CoP-9 and CoP-10 were prepared using 0.085 g Co-BTC MOF and CoFe-BTC MOF, respectively, at 170 °C for 14 h. CoP-11 was prepared using 0.3 g CoFe-MOF with 0.27 g P₄ at 160 °C for 16 h.

For NiP-20 to NiP-26 and CoP-8, the samples were synthesized via electrodeposition from aqueous electrolytes containing metal ions and sodium hypophosphite^[5,10]. Samples are thin film at the surface of conductive substrates. The general procedure for electrodeposition is as follows. A three-electrode setup was used with a conductive substrate nickel foam or carbon cloth (1 cm²) as the working electrode. The counter electrode was a cleaned graphite rod, and the reference electrode was SCE. The CV method was used to deposit the metal phosphide layers. For NiP-20 and NiP-21, the electrolytes consisted of 0.025 mol/L Ni(NO₃)₂ + 0.025 mol/L Fe(NO₃)₃ + 0.25 mol/L NaH₂PO₂ and 0.025 mol/L Ni(NO₃)₂ + 0.25 mol/L NaH₂PO₂, respectively. CV scan of −0.3−(−1) vs. SCE was applied at 5 mV/s for 8 cycles. For NiP-22 to NiP-26, the electrolyte was 0.04 mol/L Ni(NO₃)₂ + 0.01 mol/L Co(NO₃)₂ + 0.25 mol/L CH₃COONa + 0.25 mol/L NaH₂PO₂. CV scans of −0.3− (−1) vs. SCE were applied at 5 mV/s for 5, 10, 15, 20 and 25 cycles over NiP-22, NiP-23, NiP-24, NiP-25 and NiP-26, respectively.

Analysis of these data reveals several correlations. For nickel phosphides with the Ni₂P crystalline phase (NiP-5 to NiP-7), moderate crystallinity exhibits the optimum OER activity. Incorporation of Fe increases the OER activity, and the optimum extent of Fe incorporation lies in 30%−40% (NiP-1 to NiP-4, NiP-12 to NiP-13, CoP-1 to CoP-4 and CoP-9 and CoP-10). Deviation from this optimal Fe content, either higher or lower, compromises OER activity by affecting the OER kinetics, as observed by the increased Tafel slope and R_ct values. Forming Ni₂P/Fe(O)OH heterointerface can enhance the OER activity (NiP-8 to NiP-11), with an optimum thickness of the surface Fe(O)OH layer, reflected by the atomic percentage of Fe (NiP-10). Compared to samples from solvothermal phosphidation, metal phosphides prepared via electrodeposition usually exhibits higher C_dl values, which probably due to more uniform electrode surface coverage and higher specific surface area.

To ensure the reliability and repeatability of sample preparation, all these samples were synthesized at least three times, and the electrochemical measurements were performed using different batches of samples. The reported results represent the average activity performance of these phosphides. In the three electrode tests, the pH value of the electrolyte was measured using a pH value meter, and the reference electrode potential was calibrated against a new SCE before and after each test. The overpotential values and R_ct are reported as the average from more than three independent tests.

It is recommended that when using these data, users should first identify the synthesis method before making a fair comparison, as the surface states of powder-based and electrodeposited working electrode differ significantly. Typically, metal phosphides synthesized via the solvothermal phosphidization method exhibit a higher surface phosphorus content. Furthermore, when comparing with OER activity data generated from other sources, attention should be paid to the key variables including the synthetic method, test temperature, electrolyte, active material loading, and the composition. The data provided in the .bin file are directly generated without any post-treatment. Some data is provided in the .opj file, where the potential is adjusted to the RHE scale, and where iR-compensation is applied. For convenience and optimal comparability, data in the .opj file are preferably recommended.