1. The structures of selected platinum group metal (PGM) phosphides. The metal atoms displayed in grey and the phosphorus atoms displayed in red^[11]

2. Schematic illustration of the synthetic process for Ru-u₂P/PC (a)^[40] and RhP/rGO (b)^[15]

3. General synthesis procedure of MP_x@NPGC and corresponding XRD patterns (a)^[45], schematic illustration of preparation for Ru₂P@PNC/CC-900 (b)^[53]

4. TEM (a) and HRTEM (b) images of single Rh-P particle of Rh-P/CP, STEM and elemental mapping images for single Rh-P particle Rh (c) and P (d)^[56], synthesis diagram of Ru-Ru₂PΦNPC and NPC@RuO₂ (e)^[59]

5. XRD patterns for RhP_x@NPC and XPS spectra for the Rh3d and P2p regions of RhP_x@NPC catalysts (a)^[65], Partial density of states (PDOS) projected on the d orbitals of Rh atoms at the surfaces of Rh(111), Rh₂P(200) and RhP₂(¯111) (b) (The red dash and yellow solid lines indicate the Fermi level (E_F) and the location of d-bands center, respectively), electrocatalytic activities of Pt/C, Rh NS/C, and w-Rh₂P NS/C in 0.1 mol/L KOH (c), free energy pathways (∆G) for HER of P-terminated (P_T-Rh₂P (200)), Rh-terminated (Rh_T-Rh₂P (200)), and Rh (100) surfaces, respectively, under alkaline condition (d)^[71]

6. XPS results (a, b): Ir4f for IrP₂/NPC before and after the OER/HER tests^[32], schematic of the HER processes by Ru_xPNFs under alkaline conditions (c)^[75], TEM, HR-TEM images of PdP₂@CB before durability test in 1 mol/L KOH electrolyte (d) after durability test in 1 mol/L KOH electrolyte (e), and HER performance (f) of PdP₂@CB in 0.5 mol/L H₂SO₄^[69]

7. Schematic illustration of the synthesis and structure of the RuP_x/NPG electrocatalyst (a)^[77], TEM images of NC, NPC, Rh@NC, and RhP_x@NPC nanoshells (b)^[78], schematic illustration of the synthesis and structure of Rh₂P@NPC and RhP₂@NPC (c)^[65], TEM image and EDS elemental mapping of Rh, P, C and N for RhP₂@NPC (d), and SEM image of the PtNiP MNs (e)^[73]

8. XRD patterns of RuP_x synthesized in different temperatures (a)^[44], theoretical models used in DFT calculations and adopted adsorption sites of H* on the surface of these models, calculated free-energy diagram of HER at equilibrium potential for Ru₂P, RuP, and RuP₂ (b)^[46], the calculated water dissociation barrier and water dissociation pathway for RuP (121) and RuP₂ (101) surfaces (c)^[54]

9. HRTEM (a) and FFT (b) images of Ru-Ru₂PΦNPC, HER performance of Ru-Ru₂PΦNPC, Ru/C, Ru₂P/C, NPC, and 20wt% Pt/C, ∆G_H* calculated at the equilibrium potential of different models (c)^[59], high-resolution HAADF-STEM(d) and HR-TEM (f) images of a Ru-Ru₂P nanoparticle, pH dependences of the Tafel slopes of the Ru-Ru₂P/PC and Pt/C catalysts, cyclic stability of the Ru-Ru₂P/PC (f)^[40], schematic illustration of a formation process for the hollow Ru-Ru_xP-Co_xP polyhedra (g), Gibbs free energy diagram for the OER at different potentials on the surface of Co₂P and Ru-RuP_x-Co_xP models (h)^[85]

10. Pt4f core level of BPed Pt/GR with different amounts of BP (a), chemical state contents of the PtNPs as a function of BP adding amount (b), free energy diagram for HER with different Pt-P contents with ΔG_H* in each system (c)^[88], proposed photocatalytic mechanism of 0.1%-RP/g-CN for H₂ evolution (d)^[89], kinetics curves of H₂ production over Pt/g-C₃N₄ and RhP_x/g-C₃N₄-5%, cyclic running kinetics curves of H₂ production over RhP_x/g-C₃N₄-5% (e1-e2)^[90]

11. TEM (a,b), and HRTEM (c) images of Rh₂P@NC, polarization curves for Rh₂P@NC (initial and after 1000 CV scanning) and time-dependent current density curve for Rh₂P@NC under static overpotential of 20 mV for 10 h (d)^[51], electrocatalytic properties for the HER in 1.0 mol/L KOH of Ru₂P/RGO-20, Ru₂P and Pt/C (e), free-energy diagram of the HER for RGO, Ru₂P, Pt and Ru₂P/RGO-20 (f)^[81], band structure of pure RuP₂ (left) and RuP₂@NPC hybrid (right) (g)^[93], HER polarization curves of the pure metal phosphides and the physical mixture of different metal phosphides and graphene in 0.5 mol/L H₂SO₄ and 1 mol/L KOH (h)^[45]

12. Schematic illustration of the fabrication of Ru-MnFeP/NF catalysts (a), calculated charge density differences of Fe₂P-Ru and Mn₂P-Ru structures (b)^[98], high-resolution XPS spectra of Ni2p, Fe2p and P2p in the Ru-NiFe-P and the NiFe-P (c), the absorption modeled surfaces of Ru-NiFe-P (d), calculated ΔG_H* for Ru-NiFe-P, NiFe-P, Ru-Ni-P, Ni-P, Ru-Fe-P and Fe-P (e), total density of states of Ru-NiFe-P and NiFe-P (f)^[99]

13. HRTEM image of PdNP-CN (a), HAADF-STEM images of PdPNP-CN (b) and PdPSA-CN (c), the geometry structures of PdNP-CN (d), PdPNP-CN (e) and PdPSA-CN (f), Pd K-edge XANES spectra (g) and the corresponding k³-weighted FT spectra at R(h) and k(i) space^{[ 103]}, EXAFS spectra (j) of RuCl₃@HPN and Ru SAs@PN, Wavelet transform (k) of Ru SAs@PN, Ru foil and RuCl₃@HPN samples, N K edge (l) and P L edge (m) NEXAFS spectra, ³¹P solid state MAS NMR spectra at room temperature using a direct acquisition with proton decoupling of PN and RuβSAs@PN (n)^[104]

14. In situ silver K-edge XANES (a) and EXAFS spectra (b) of AgP₂ NCs, AgO, Ag₂O, and Ag foil, Faradaic efficiency of the CO and CO:H₂ ratio as a function of Ag^δ+ in AgP₂ and Ag (c), linear combination of AgO, Ag₂O, and Ag spectra (solid line) compared to the raw Ag K-edge (d), Ag K-edge XANES spectra of AgP₂ NCs with respect to CRR time under a constant applied potential of -0.8 V (vs. RHE) (e), Ag K-edge spectra of AgO and Ag₂O references before and after CRR at -0.8 V (vs. RHE) for 50 s (f)^[38]

15. Schematic illustration of the formation of Ni@Ni₂P-Ru HNRs (a), Ni K-edge XANES spectra (b) and Fourier transformed k³-weighted EXAFS spectra of Ni@Ni₂P-Ru, Ni@Ni₂P, and reference Ni foil (c), Ru K-edge XANES spectra of Ni@Ni₂P-Ru and reference Ru foil (d), dependence of the Ru(0) and Ru(IV) atomic fractions of the Ni@Ni₂P-Ru HNRs as a function of photon energy (e)^[108], Ni2p XPS comparison (f) and Ni L edge XANES comparison between Ni₅P₄-Ru and Ni₅P₄ (g), XANES (h) and EXAFS (i) results of Ni₅P₄-Ru, Ni₅P₄, Ni foil, and NiO at Ni K edge, respectively, Ru K-edge XAFS spectra (j) and the Ru K-edge k²-weighted EXAFS profiles of Ru foil, Ni₅P₄-Ru, and RuO₂ (k)^[97]