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Designing highly active, durable, and nonprecious metal‐based bifunctional electrocatalysts for overall water electrolysis is of urgent scientific importance to realize the sustainable hydrogen production, which remains a grand challenge. Herein, an innovative approach is demonstrated to synthesize flower‐like 3D homogenous trimetallic Mn, Ni, Co phosphide catalysts directly on nickel foam via electrodeposition followed by plasma phosphidation. The electrochemical activity of the catalysts with varying Mn:Ni:Co ratios is assessed to identify the optimal composition, demonstrating that the equimolar trimetallic phosphide yields an outstanding HER catalytic performance with a current density of 10 mA cm−2 at an ultra‐low overpotential of ~14 mV, outperforming the best reported electrocatalysts. This is asserted by the DFT calculations, revealing strong interaction of the metals and the P atom, resulting in enhanced water activation and optimized GH* values for the HER process. Moreover, this optimal composition appreciably catalyzes the OER by exposing more intrinsic active species in‐situ formed on the catalyst surface during the OER. Therefore, the Mn1‐Ni1‐Co1‐P‐(O)/NF catalyst exhibits a decreased overpotential of ~289 mV at 10 mA cm−2. More importantly, the electrocatalyst sustains perfect durability up to 48 h at a current density of 10 mA cm−2 and continued 5000 cycling stability for both HER and OER. Meanwhile, the assembled MNC‐P/NF||MNC‐P/NF full water electrolyzer system attains an extremely low cell voltage of 1.48 V at 10 mA cm−2. Significantly, the robust stability of the overall system results in a remarkable current retention of ~96% after a continuous 50‐h run. Therefore, this study provides a facile design and a scalable construction of superb bifunctional ternary MNC‐phosphide electrocatalysts for efficient electrochemical energy production systems.

No abstract

Electrochemical energy storage (EES) technologies are playing a leading role in the global effort to address the energy challenges. Current EES systems are limited by their energy density, capacity, and cycling stability. Some of those limitations arise from nanoscale phenomena, which are not fully understood or accounted for. Electrochemical activation (ECA), an often-overlooked process, creates more active sites on the electrode material and boosts the activity of the system to achieve a higher storage capacity. Herein, the ECA of bimetallic Ni–Co oxyphosphides is investigated via a plethora of spectroscopic techniques, including transmission electron microscopy enhanced by multivariate statistical analysis as a tool to better analyze the obtained spectra. Interestingly, ECA induces an in situ reconstruction of the pre-electrode via phosphorus leaching, together with accelerated surface segregation of the reconstructed Ni and Co species. The electrodes with reconstructed composition showed 110% higher supercapacitive performance than their pre-electrode counterparts. Thanks to the electrochemical optimization approach, a hybrid device has been assembled with a superb performance. The device exhibits energy density values comparable with batteries: 89 W h kg–1 at a power density of 848 W kg–1 with an excellent stability over 10,000 galvanic charge–discharge cycles as manifested by the steady capacitive retention (94.2–100.9%) even during the last 1000 cycles.