Electrocatalytic hydrogen production by water splitting is highly energy-intensive due to poor electrocatalysts and sluggish four-electron oxygen evolution reaction (OER) kinetics. Herein, MnO₂ and sulfur-doped MnO₂ (S-MnO₂) are prepared by a simple hydrothermal method. The results show that S-MnO₂ exhibits a higher OER activity than MnO₂ because the sulfur doping gives rise to more Mn³⁺ active sites, oxygen vacancies (V_O) and electrochemically active surface areas. Density functional theory (DFT) calculation further confirms that the abundant V_O leads to a higher surface energy of S-MnO₂, which is conducive to the adsorptions of H₂O and OH^- on Mn³⁺ sites. Moreover, formaldehyde oxidation reaction (FOR) is employed to substitute for sluggish OER to improve hydrogen evolution reaction (HER). Compared to OER-based electrolyzer (3.354 V), the cell voltage of FOR-based electrolyzer (2.778 V) at 100 mA cm⁻² has decreased by 17.17 %, and the Faradic efficiency of hydrogen production increases from 89.6 % to 98.6 %. The results indicates that to produce the same amount of hydrogen, 17.17 % of electric energy can be economized. Thus the cost of hydrogen production decreases greatly. The HER efficiency is greatly improved because FOR has faster kinetics than OER. Meanwhile, after running for 2 h at 1.75 V, 52 % of formaldehyde has been degraded. The results demonstrate that the innovative electrolyzer can not only greatly improve the HER efficiency, but also efficiently degrade formaldehyde pollutants.

由于较差的电催化剂和缓慢的四电子析氧反应 (OER) 动力学，通过水分解的电催化制氢是高能量密集型的。在此，通过简单的水热法制备MnO ₂和硫掺杂的MnO ₂ (S-MnO _{2 )。}结果表明，S-MnO ₂表现出比MnO ₂更高的OER活性，因为硫掺杂产生了更多的Mn ³⁺活性位点、氧空位(V _O )和电化学活性表面积。密度泛函理论（DFT）计算进一步证实了丰富的VO_导致S-MnO _{2具有更高的表面能}, 有利于 H ₂ O 和 OH ^-在 Mn ³⁺位点上的吸附。此外，甲醛氧化反应（FOR）被用来替代缓慢的OER，以改善析氢反应（HER）。与基于 OER 的电解槽 (3.354 V) 相比，基于 FOR 的电解槽的电池电压 (2.778 V) 在 100 mA cm ^-2下降了 17.17%，制氢的法拉第效率从 89.6% 提高到 98.6%。结果表明，生产同样数量的氢气，可节约17.17%的电能。因此制氢成本大大降低。HER 效率大大提高，因为 FOR 的动力学比 OER 更快。同时，在 1.75 V 下运行 2 小时后，52% 的甲醛已被降解。结果表明，创新的电解槽不仅可以大大提高HER效率，还可以有效降解甲醛污染物。