Acoustically‐Induced Water Frustration for Enhanced Hydrogen Evolution Reaction in Neutral Electrolytes

Abstract

Despite its appeal of green H 2 production using energy from renewable sources, water electrolysis currently only accounts for a small percentage of global H 2 production due to the need for expensive electrocatalysts to compensate for Ohmic losses associated with the kinetic overpotential of the system. [4][5][6] At present, H 2 production via electrolysis is predominantly carried out in strong acidic/alkaline electrolytes using state-of-the-art platinum group metal (PGM) electrocatalysts, which enables hydrogen evolution reactions (HER) to be conducted at the lowest onset potential, albeit at practically insurmountable industrial costs due to the metal's scarcity. [7,8] To attain industrially-relevant current densities (200-500 mA cm −2 ), an overpotential between 1.8 and 2.5 V is typically required. [9] At these levels though, acidic electrolytes-while providing an abundant source of protons (H + ) and hydronium (H 3 O + ) ions-produce acid fog under high temperatures that can corrode the electrolyzer and contaminate the product. [10] Alkaline electrolysis, on the other hand, is commonly plagued by unstable electrocatalysts and the need for expensive pH-tolerant membranes. [11][12][13] It is therefore desirable to carry out electrolysis in neutral or near-neutral electrolytes (pH 5-9) with non-PGM electrocatalysts. [14] The HER rate under these conditions is, nevertheless, significantly lower than those for electrolytes with extreme pH levels. In addition to diffusion limitations, this is due to the rapid consumption of H 3 O + , which creates a bottleneck that limits the extent of reaction until higher overpotentials are able to drive H 2 O reduction. [10,[15][16][17] Even with the best electrodes (i.e., PGMs), H 2 production is several orders of magnitude lower under neutral conditions, [7] such that the overpotential required to reach a current density of −4 mA cm −2 exceeds 0.25 V in a 0.1 M KClO 4 electrolyte compared to as little as 30 mV in 0.5 M H 2 SO 4 . [18,19] Similarly poor performance is obtained with the use of nickel-based electrocatalysts, which are generally favored for alkaline conditions, given their affinity for OH − adsorption. [20] To circumvent these limitations, novel electrocatalysts have been designed, in which the electrode is doped to tailor its catalytic sites for both H* and OH* adsorption to complement the electrolytic conditions, [21][22][23] or through the introduction of complex architectures that facilitate more favorable local pH environments, [24] although these strategies A novel strategy utilizing high-frequency (10 MHz) hybrid sound waves to dramatically enhance hydrogen evolution reactions (HER) in notoriously difficult neutral electrolytes by modifying their network coordination state is presented. Herein, the practical limitations associated with existing electrolyzer technology is addressed, including the need for highly corrosive electrolytes and expensive electrocatalysts, by redefining conceptually-poor hydrogen electrocatalysts in neutral electrolytes. The impro...

From brew to clean fuel: harnessing distillery wastewater for electrolysis H2 generation using nano scale nickle selenide water oxidation catalysts

“…To mitigate the bubbling effect at the cathode, effective approaches involve the incorporation of ultrasonic treatment 73 or cavitation treatment 74 at the cathode. For instance, a study conducted by Ehrnst and colleagues 73 showcased an enhancement in the HER performance. This improvement stems from the intense local electromechanical coupling induced by acoustic forcing.…”

Free-standing multi-hierarchical MoC-based catalyst for pH-universal hydrogen evolution reaction at ultra-high current density

“…The potential of the HER at a current density of 10 mA cm −2 is utilized as the reference potential for EIS. To estimate the electrochemically active surface area of the catalysts, continuous cyclic voltammetry (CV) was performed within the non-faradaic potential range (0.1 to 0.2 V vs. RHE) at various scan rates (20,40,60,80, and 100 mV s −1 ).…”

“…18 However, the efficiency of MoC-based catalysts in improving the HER reaction decreases significantly when exposed to alkaline and neutral environments compared to their performance in acidic media. 19,20 This is attributed to the involvement of two additional processes related to water dissociation in hindering rapid reaction kinetics within the HER mechanism. 21 The adsorption energy of hydroxyl ions (OH*) plays a crucial role in determining the dissociation rate of water, and subsequently, the production of H* intermediates, which are essential for enhancing alkaline and neutral HER activity.…”

New age chloride shielding strategies for corrosion resistant direct seawater splitting

“…Surface acoustic waves, which have innumerable applications, 132,133 have been recently implemented in the field of water splitting to enhance the HER process. 134 The approach involved the application of high frequency (10 MHz) surface and bulk acoustic waves, known as surface reflected bulk waves (SRBWs), which improved the HER performance with increased current density by 14-fold. The mechanism follows the weakening of the intramolecular hydrogen bonding by SRBW excitation, enabling the better accessibility of free water molecules at the electrode; also, the convective flow leads to better mass diffusion and electron transfer.…”